Fix project creation dropdown regression without changing project routes

[raphaeltm]

Summary

• Restored projects routing behavior to what it was before PR Add project-mode create flow and top-level navbar links #110 by removing accidental route wiring to workspace screens.
• Kept top-level navbar links in UserMenu intact.
• Updated project creation form to use workspace-style repository and branch behavior:
  • repository uses searchable RepoSelector
  • branch list is fetched from listBranches after repo selection
  • repository submit value is normalized to owner/repo
• Added route regression coverage and updated project/workspace page tests.

Validation

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

Validation run details:

• pnpm --filter @simple-agent-manager/web lint
• pnpm --filter @simple-agent-manager/web typecheck
• pnpm --filter @simple-agent-manager/web test
• pnpm --filter @simple-agent-manager/web test -- tests/unit/app-routes.test.tsx tests/unit/pages/projects.test.tsx tests/unit/pages/create-workspace.test.tsx
• Mobile viewport verification screenshot: .codex/tmp/playwright-screenshots/project-form-mobile-harness.png

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; existing internal API utilities (listRepositories, listBranches) were reused.

Codebase Impact Analysis

• apps/web/src/App.tsx
• apps/web/src/components/project/ProjectForm.tsx
• apps/web/src/pages/CreateWorkspace.tsx
• apps/web/tests/unit/app-routes.test.tsx
• apps/web/tests/unit/pages/projects.test.tsx
• apps/web/tests/unit/pages/create-workspace.test.tsx

Documentation & Specs

• tasks/backlog/2026-02-18-project-form-dropdown-regression-fix.md
• tasks/backlog/2026-02-18-project-creation-dropdowns-and-navbar-links.md

Constitution & Risk Check

• Checked constitution alignment for Principle XI (No Hardcoded Values).
• Change scope is UI routing/form behavior only; no new hardcoded URLs, limits, timeouts, or identifiers were introduced.
• Primary risk was route regression and incorrect project payloads; mitigated with route and form tests.