Codex Desktop: add independent user labels for threads and projects

Feature request

Codex Desktop can become hard to manage when the sidebar contains many projects and many old or paused conversations. I would like a first-class way to mark both:

• individual threads/sessions
• projects/workspaces

The important part is that these should be independent labels or colored markers, not just renaming a thread or project. Renaming loses the original title/context and does not work well for triage states such as "deferred", "blocked", "follow up later", or "active".

Desired behavior

• Let users assign a small text label and optional color to a thread.
• Let users assign a small text label and optional color to a project/workspace.
• Keep labels separate from thread names, project names, and git metadata.
• Preserve labels across thread read/list/resume/fork/rollback flows.
• Allow clearing labels explicitly.
• Give clients enough protocol support to render sidebar badges/chips and filter or group later.

Prototype branch

I pushed a prototype branch from my fork:

https://github.com/openai/codex/compare/main...chenk0527:thread-user-labels

I could not open a PR directly because this repository currently limits PR creation to collaborators, but the branch is available for review.

What the branch currently does:

• adds a UserLabel { text, color } protocol shape
• exposes userLabel on thread responses
• extends thread/metadata/update to set or clear a thread label independently from the thread name
• adds project/metadata/update and project/metadata/list
• persists thread labels and project labels in SQLite state
• preserves thread labels during rollout reconciliation
• regenerates app-server JSON and TypeScript schemas
• adds coverage for set/read/list/clear behavior

Validation run on the branch

• just write-app-server-schema
• just test -p codex-app-server-protocol
• just test -p codex-thread-store
• just test -p codex-state
• cargo build -p codex-cli --bin codex
• cargo build -p codex-rmcp-client --bin test_stdio_server
• just test -p codex-app-server project_metadata thread_metadata_update
• just test -p codex-app-server (917 passed, 1 skipped)
• just fmt