Make sticky comments toggleable (enable/disable per repo)

Summary

Add an orchestrator input to enable/disable sticky comments per-repo (or per-invocation), so a review can post a new comment each run instead of updating one in place.

Motivation

@wezell wants sticky comments off for his OVH repo. He prefers the interleaved history timeline on the PR: review → commit with fix → next review → commit, etc. Sticky comments collapse that into a single self-updating comment, erasing the back-and-forth that he uses to follow how the PR evolved.

Today sticky behavior is effectively always-on:

• Anthropic path (claude-executor.yml) hardcodes use_sticky_comment: "true".
• Bedrock generic (bedrock-generic-executor.yml) and Codex (codex-executor.yml) always run their /tmp find-or-update sticky helper.

There's a sticky_namespace input but no way to turn stickiness off.

Proposal

Add a boolean sticky_comments input to claude-orchestrator.yml (default true to preserve current behavior) and thread it to all three executor paths:

• Anthropic: map to use_sticky_comment: ${{ inputs.sticky_comments }}.
• Bedrock generic / Codex: when false, skip the find-or-update step and just create a fresh comment (post instead of patch).

Repos that want the timeline (OVH) set sticky_comments: false in their caller workflow.

Acceptance criteria

• sticky_comments input on the orchestrator, default true (no behavior change for existing consumers).
• When false, each review run posts a new PR comment on all three executor paths.
• When true, behavior is unchanged (single updating comment, sticky_namespace still respected).
• Documented in CLAUDE.md / ARCHITECTURE.md alongside sticky_namespace.

Start by reading claude-orchestrator.yml, then compare claude-executor.yml, bedrock-generic-executor.yml, and codex-executor.yml to trace sticky_comments and sticky_namespace. Verify how each path finds, updates, or posts comments. Done means the default preserves sticky behavior, false posts a new comment on all three paths, and the option is documented in CLAUDE.md or ARCHITECTURE.md.