fix: prevent project task-form typing crash

[raphaeltm]

Summary

• Fix task form input handling by capturing field values before functional state updates, preventing stale synthetic event access during typing.
• Add dedicated TaskForm regression tests for multi-character typing across text, textarea, number, select, and optional hint fields.
• Add project-page integration regression coverage for realistic multi-keystroke typing in the New Task flow.
• Update AGENTS.md and CLAUDE.md with required UI form behavior test rules to prevent recurrence.

Validation

• pnpm lint
• pnpm typecheck
• pnpm test
• Additional validation run (if applicable)
• Mobile and desktop verification notes added for UI changes

Additional validation run details:

• pnpm install
• pnpm --filter @simple-agent-manager/shared build
• pnpm --filter @simple-agent-manager/ui build
• pnpm --filter @simple-agent-manager/acp-client build
• pnpm --filter @simple-agent-manager/terminal build
• pnpm --filter @simple-agent-manager/web typecheck
• pnpm --filter @simple-agent-manager/web lint
• pnpm --filter @simple-agent-manager/web test

UI Compliance Checklist (Required for UI changes)

• Mobile-first layout verified
• Accessibility checks completed
• Shared UI components used or exception documented

Exceptions (If any)

• Scope: N/A
• Rationale: N/A
• Expiration: N/A

Agent Preflight (Required)

• Preflight completed before code changes

Classification

• external-api-change
• cross-component-change
• business-logic-change
• public-surface-change
• docs-sync-change
• security-sensitive-change
• ui-change
• infra-change

External References

N/A: no external API contract changes; code and existing project docs were sufficient.

Codebase Impact Analysis

• apps/web/src/components/project/TaskForm.tsx (task form state update path)
• apps/web/tests/unit/components/project/task-form.test.tsx (new focused regression coverage)
• apps/web/tests/unit/pages/project.test.tsx (integration flow coverage)
• AGENTS.md, CLAUDE.md (testing guidance hardening)

Documentation & Specs

• Updated: AGENTS.md
• Updated: CLAUDE.md
• Specs: N/A (no spec-doc updates needed for this bugfix scope)

Constitution & Risk Check

• Checked constitution principles relevant to this change, including Principle XI (No Hardcoded Values).
• No new hardcoded URLs/timeouts/limits/identifiers introduced.
• Primary risk addressed: user-facing form crash during normal typing; mitigated via code fix + unit/integration regression tests.