Docs: bring the architecture doc up to date with main

[mchwang]

Who this is for: anyone who reads docs/architecture.md to learn what codeboost does today.
What it does: brings the architecture overview up to date with main at 7edf36d. Docs only, no code change.

Summary

The doc still described the runner as "built, not connected". With a runner block in review.json, the whole loop after planning now runs. This PR records that.

Section	Change
Summary	Three levels: in use, in use with a github block (planning), and in use with the opt-in runner block (start/resume, publishing, merging the task's own PR, closing PRs on cancel).
Module table	New rows: planning agent, workspace, diagnostics. The merge coordinator merges the task's published PR (#121). Ask and planning share one read-only container runner (#117). Status wording is now the same in every row.
Flows	Flow 3 merges the task's own PR. Flow 4 is in use: when it publishes, and how commits that were already on the branch show as Unplanned (#113).
Trust rules	Branch push limits (#101) and the pre-launch tree check (#100).
Stored data	publish_outcomes, schema version 11, planning owner token.
Roadmap	E done (#45). F lists everything merged; #130 in review. G unblocked. H4b (#108) after #130. New row for test reliability (#129).
Known limits	No screen controls for the runner or planning yet. Publishing needs github.baseBranch. The runner does not check who wrote an issue (#108). Claude-only (#93).

How this was checked

• Every merged PR since F2b: connect the real lane D workspace (#87, part 1) #92 was read for its effect on the doc, and every status claim was checked against main (for example, which modules production builds, the store's tables and schema version).
• This branch includes the edits that D: refuse Codex in every phase (#93, option 3) #106, F: publish a finished task's pull request in production (#103) #110, F: close a cancelled task's pull requests (#111) #115, F: run plan suggestions through lane D in planning's own worker (#117, part 2) #120 and F: redraft the current plan through lane D (#124) #125 made to the doc on main. One conflict, in the module table, was resolved by keeping both sides.

Test this doc with a reader

The doc ends with four questions a new reader should answer from the Summary and the layer map alone. Please try them before approving.

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