build: prepare ContextIME 0.5.4 preview

[kun002]

Scope

Bump the preview identity to 0.5.4-preview so the merged M5.5 manual-term work ships in its own verifiable installer, following the established version-bump pattern:

• native/contextime.identity.json: version 0.5.4-preview, numeric 0.5.4.0, install leaf contextime-0.5.4-preview
• add apply-contextime-0.5.4-fixes.ps1 (0.5.3 → 0.5.4 installer string bump plus an M5.5 rollout report listing add_term / remove_entry)
• add the ContextIME Native Preview 0.5.4 workflow; the cumulative fix chain still applies every earlier version script including 0.5.3
• retire the 0.5.3 workflow's pull_request trigger (keeps workflow_dispatch), matching how 0.5.2 was retired

No product source changes.

Verification status

Layer	Status	Evidence
implemented	complete	identity bump, fix script, workflow chain audit assertions updated (management operations now 7)
built	pending	this PR's build-contextime-preview-0-5-4 run
CI	pending	installer manifest, isolation audit, and hash report on this PR