chore: add AGENTS.md, helper scripts, codex templates, and CI

.claude/agents/codex.md

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+# Project Agent Handoff
+
+Use AGENTS.md at repo root as the source of truth for coding rules and guardrails.
+
+Key Rules
+- Code first, concise rationale after. If uncertain, say "Uncertain:".
+- Keep diffs minimal; follow existing patterns and `analysis_options.yaml`.
+- Validate with `scripts/check.sh` (format/analyze/test) before completion.
+- Ask for approval before dependency changes, build config edits, or network access.
+
+Templates
+- Task and PR templates are in `AGENTS.md` and `doc/agents/codex_prompt_templates.md`.
+

.github/workflows/flutter_ci.yml

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+name: Flutter CI
+
+on:
+  pull_request:
+  push:
+    branches: [ main, master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+
+      - name: Flutter Pub Get
+        run: flutter pub get
+
+      - name: Format check
+        run: dart format --output=none --set-exit-if-changed .
+
+      - name: Analyze
+        run: flutter analyze
+
+      - name: Test
+        run: flutter test
+

AGENTS.md

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+Codex Agent Guide for SubManager
+
+Scope
+- Applies to the entire repository unless a more specific rule exists deeper in the tree.
+- Precedence: project AGENTS.md > project .claude/agents > user ~/.claude > default Codex CLI rules. Direct system/developer instructions always win.
+
+Goals
+- Accelerate small, safe changes with consistent quality.
+- Keep diffs minimal, focused, and aligned with Flutter best practices.
+
+Guardrails
+- Workspace only: modify files within this repo. Ask before adding dependencies or using network.
+- Safety: avoid destructive actions (file deletions, rewrites, config changes) unless explicitly requested.
+- Responses: be concise; code first, short rationale after. If uncertain, prefix with "Uncertain:". If multiple viable solutions, show the top 2 briefly.
+- Planning: for multi‑step tasks, maintain an update_plan with exactly one in_progress step.
+
+Coding Standards
+- Language: Dart/Flutter (SDK >= 3.0). Respect `analysis_options.yaml` (flutter_lints baseline).
+- Style/format: use `dart format .` and keep changes minimal. Avoid one‑letter variable names; avoid inline comments unless requested.
+- Structure: follow existing file/module patterns and naming. Do not introduce new frameworks or architectural shifts without approval.
+- Tests: add or update tests when behavior changes or bugs are fixed (if feasible). Keep tests scoped to the change.
+
+Validation
+- Always run local checks via `scripts/check.sh` before proposing completion:
+  - formatting check: `dart format --set-exit-if-changed .`
+  - static analysis: `flutter analyze`
+  - unit/widget tests: `flutter test` (ok if none exist)
+- UI changes: include brief description of visual impact; screenshots if readily available by the user.
+
+Sensitive Areas (require explicit approval)
+- Android/iOS/macOS build configs, signing, bundle identifiers, Gradle/Kotlin/Swift project settings.
+- Dependency graph changes (pubspec.yaml add/remove/upgrade).
+- Network access, calling external APIs, or adding secrets.
+
+Operational Conventions
+- Branch naming: `codex/<type>-<slug>` (e.g., `codex/fix-url-matcher`).
+- Commits: Conventional Commits preferred (e.g., `fix: correct url matching for X`).
+- PR description template:
+  - Summary: what/why
+  - Changes: key files and decisions
+  - Validation: how verified (analyze/tests/manual)
+  - Risk & Rollback: potential impact and quick rollback steps
+
+Task Template (author-provided)
+---
+Next: <what to do>
+Complexity: simple | medium | complex
+
+Context
+- Problem / goal:
+- Constraints / non‑goals:
+- Repro or commands:
+
+Done When
+- [ ] Behavior verified (`scripts/check.sh` passes)
+- [ ] Tests/docs updated if applicable
+---
+
+Commands
+- Lint/analyze/tests: `scripts/check.sh`
+- Auto‑format: `scripts/fix.sh`
+
+References & External Facts
+- Prefer official docs and code‑local references. If citing sources, include plain URLs or file paths in PR descriptions (avoid footnote citation syntaxes).
+
+Notes from ~/.claude (adapted)
+- Few‑shot examples improve accuracy; include small before/after or sample input→output when helpful.
+- Use structured thinking internally; present only concise, actionable outputs here.
+

doc/agents/codex_prompt_templates.md

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+Codex Prompt Templates
+
+Note
+- Keep prompts concise and specific. Include before/after or small input→output examples when helpful.
+- Use the Task Template in AGENTS.md for clarity and a crisp definition of Done.
+
+Next Task Format (from ~/.claude)
+---
+Next: <what to do>
+Complexity: simple | medium | complex
+---
+
+Bugfix Prompt
+---
+Context
+- Problem: <symptoms and scope>
+- Repro: <steps/command>
+- Observed: <actual result>
+- Expected: <desired result>
+- Constraints / Non‑goals: <limits>
+
+Done When
+- scripts/check.sh passes; behavior verified via repro
+- Tests/docs updated if applicable
+---
+
+Small Feature Prompt
+---
+Context
+- Goal: <user‑visible behavior>
+- Entry points: <screens/routes/widgets>
+- Data/State impact: <provider/models/side effects>
+- Constraints / Non‑goals: <limits>
+
+Done When
+- Feature is reachable and works
+- scripts/check.sh passes; minimal tests if feasible
+---
+
+Refactor Prompt (No Behavior Change)
+---
+Context
+- Target: <files/modules>
+- Motivation: <readability/duplication/perf>
+- Safety: <no logic change; add tests if risky>
+
+Done When
+- Same behavior; cleaner structure
+- scripts/check.sh passes
+---
+
+UI Change Prompt
+---
+Context
+- Screen/Widget: <where>
+- Visual Goal: <what changes>
+- Theming/Adaptivity: <light/dark/platform>
+
+Done When
+- Visual change implemented; screenshots added in PR by human
+- scripts/check.sh passes
+---
+
+Code Review Aid
+---
+- Summarize intent and key diffs
+- Verify formatting, analysis, and tests pass
+- Flag risks; suggest targeted follow‑ups
+---
+

scripts/check.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+echo "==> Formatting check"
+if command -v dart >/dev/null 2>&1; then
+  dart format --output=none --set-exit-if-changed .
+else
+  echo "dart not found in PATH" >&2
+  exit 1
+fi
+
+echo "==> Static analysis"
+flutter analyze
+
+echo "==> Tests"
+flutter test
+
+echo "\nAll checks passed."
+

scripts/fix.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+echo "==> Formatting code"
+dart format .
+
+echo "Formatting complete."
+