chore: use repository-local Codex worktrees

[jBernavaPrah]

Summary

• Replace the obsolete provider-specific worktree ignore with a repository-local .codex/worktrees/ ignore so task worktrees stay with their owning repository.
• Replace the camera conversion iteration with the Rust stable form required by the current Clippy gate. Incomplete trailing pixel bytes remain ignored.

Validation

• git diff --check
• cargo fmt --check
• cargo test (35 passed)
• cargo clippy --all-targets -- -D warnings
• zero tracked matches for retired provider names and paths
• live migration worktree moved under this repository's .codex/worktrees/ directory