fix(map-codebase): pass current date to mapper agents to fix wrong Analysis Date (#2298)

The `cmdInitMapCodebase` / `initMapCodebase` init handlers did not
include `date` or `timestamp` fields in their JSON output, unlike
`init quick` and `init todo` which both provide them.

Because the mapper agents had no reliable date source, they were forced
to guess the date from model training data, producing incorrect
Analysis Date values (e.g. 2025-07-15 instead of the actual date) in
all seven `.planning/codebase/*.md` documents.

Changes:
- Add `date` and `timestamp` to `cmdInitMapCodebase` (init.cjs) and
  `initMapCodebase` (init.ts)
- Pass `{date}` into each mapper agent prompt via the workflow
- Update agent definition to use the prompt-provided date instead of
  guessing
- Cover sequential_mapping fallback path as well

agents/gsd-codebase-mapper.md

@@ -160,7 +160,7 @@ Write document(s) to `.planning/codebase/` using the templates below.
 **Document naming:** UPPERCASE.md (e.g., STACK.md, ARCHITECTURE.md)
 
 **Template filling:**
-1. Replace `[YYYY-MM-DD]` with current date
+1. Replace `[YYYY-MM-DD]` with the date provided in your prompt (the `Today's date:` line). NEVER guess or infer the date — always use the exact date from the prompt.
 2. Replace `[Placeholder text]` with findings from exploration
 3. If something is not found, use "Not detected" or "Not applicable"
 4. Always include file paths with backticks