Bring the docs back in line with what the checkout does

[owenpkent]

Summary

A sweep after the update client, the candidate workflow and the bill of materials. Every change is either a claim that had stopped being true, or something the checkout does that nothing documented. Docs only; no code touched.

Claims that were actively wrong

Both falsified by #16:

• build-windows.md: the build inventories are "not a complete third-party license inventory or SBOM"
• build-windows.md: "A release-ready third-party license inventory and SBOM remain separate work"

And in release-plan.md, the in-app check was still described as deferred after #15 shipped it.

One that needed splitting rather than deleting

The scope freeze listed "auto-update" flatly. That is now misleading in both directions, so it reads:

Updating is inside the freeze only as far as it goes today: the check is automatic, and installing never is. Nothing is downloaded, replaced or restarted without someone asking for it, and a silent background update stays out of scope.

More useful than either "deferred" or silence, and it holds the line that matters.

Gaps where the code had no documentation

• README listed update in the commands table and explained it nowhere. It now has a section: what is verified before anything runs, and that an update never closes a running Offloader — the guarantee, not a limitation. docs/updates.md added to the documentation index.
• The agent guide's code map listed none of the installation or update modules, so finding where maintenance lives meant grepping. It now names installation.py, installation_lock.py, update.py and gui/updates.py together with the rule binding them: neither may force-close a running transfer. Its start-here list points at build-windows.md and updates.md, and states that a build being implemented is not a release being possible — the distinction the plan keeps having to restate.
• ROADMAP still listed "Windows installer and code signing" as future work when the packaging is implemented. Replaced with what is actually left, none of which is code: the hardware token, a clean machine, and the Qt LGPL/GPL redistribution decision the notices file flags on every build.

Validation record

Added a dated source-validation entry (855 passed, 12 skipped, lint clean, sdist checked), labelled as exactly that: nothing was frozen, signed or installed, so it establishes none of the gates it sits above. Per AGENTS.md, counts come from an actual run and a source run is not bundle qualification.

Scope note

shellicon.py, shellmenu.py and gui/file_list.py are not in the code map here, because they exist only on the other stack (#11, #12). Documenting them on this branch would describe modules the branch does not contain. They need their own sweep on that stack — happy to do it, but it has to be a separate PR or the two conflict.

Checked, not assumed

• All 68 relative links across the markdown docs resolve
• Every CLI subcommand (offload, report, verify, info, gui, update, resolve, control) appears in the commands table
• Every --flag of offload is mentioned in the README
• No remaining "deferred / separate work / not implemented" claims about anything now implemented; the two that remain (release qualification pending, destination coordination unimplemented) are both accurate
• Diff is documentation only

[owenpkent]

Reviewed the five documentation changes against the implementation in this head, including Windows build/release status, updater behavior, profile/media-tool boundaries, and the stated safety limits.

No independent non-sensitive code defect is introduced by this documentation-only diff. One newly repeated updater-protection claim needs to wait for the underlying correction identified on #13; its exact claim and call-path evidence are included in the private updater/documentation notes under SECURITY.md.

Validation: static documentation/code consistency review and git diff --check, which passed. Recorded CI is green. No local test suite was rerun for this documentation-only review, and the review does not treat implemented packaging scripts as evidence that signing or clean-machine qualification has passed.