ci-assign-id --help says "no file rename"; the command renames files

[explosivebit]

What is wrong

forgeplan ci-assign-id --help describes the command as rewriting frontmatter only:

Walks .forgeplan/**/*.md in --head, finds candidates with assigned_number: null, computes
next = max(assigned_number)+1 per kind from --base git ref, rewrites frontmatter (no file
rename - Phase 2.1).

Source of that string: crates/forgeplan-cli/src/main.rs:770-777.

On 0.37.0 the command does rename. A fresh assignment reports action: "renamed_and_assigned" and
the file is moved from <kind>-<slug>.md to <KIND>-<NNN>-<slug>.md (via git mv with a
std::fs::rename fallback). The module header of the implementation documents the later phase -
crates/forgeplan-cli/src/commands/ci_assign_id.rs:33-48 (Phase 2.2) - and apply_plan
(ci_assign_id.rs:758-987) performs the rename. Unit tests assert the action at
ci_assign_id.rs:2493-2522 and 2729-2733.

In other words: the help string is a Phase 2.1 statement that survived into a Phase 2.2 binary.

Evidence

Reproduced on 0.37.0 in a throwaway git workspace:

$ forgeplan ci-assign-id --head HEAD --base HEAD --json
  "assignments": [ { "slug": "prd-widget-auth",
                     "action": "renamed_and_assigned",
                     "assigned_number": 1,
                     "path": ".../PRD-001-widget-auth.md" } ]

$ ls .forgeplan/prds/
PRD-001-widget-auth.md          # was prd-widget-auth.md

• help string: main.rs:770-777; implementation: ci_assign_id.rs:33-48, 758-987
• documented behaviour mismatch is also acknowledged in
  website/src/content/docs/docs/cli/ci-assign-id.md, which describes the rename it observes rather
  than the help text it is given

Fix

Drop "no file rename - Phase 2.1" from the description, or state the rename. A caller who scripted
around "frontmatter only" will find their paths rewritten.

Revisit trigger

Act if any release note describes ci-assign-id as frontmatter-only, or if a downstream script
(hooks, other workflows) resolves artifact paths before running it.