Clarify current v2 status and remaining stable release gates

[LeiterConsulting]

v2 is already the default framework on main, but the public status still described the completed native application follow-up as pending and omitted the owner's successful Cursor, VS Code and Codex use.

Clarify current-main versus the fixed preview tag, correct the completed deployment status, and record the host feedback explicitly as owner-reported use. VS Code's agent/extension identity and detailed host trial evidence remain unspecified. Add the concrete remaining checklist for a stable 2.0.0 release while preserving historical records and release identities.

Validation:

• Repository validation passed: 10 modules, 316 supported local links.
• Local unittest discovery: 114 discovered, 112 passed, two host symlink-capability skips; whitespace checks passed.
• Candidate push CI and PR CI passed at 8de2854. All four Windows/Linux Python 3.10/3.13 jobs in each run passed all 114 tests without skips.
• Merged main 19b3e1b has the identical tree 4ac2eac90a80b7e6f67c961be6d157a5b510354e. Merged-main CI also passed all 114 tests without skips in all four jobs.

The update covers README.md, docs/v2/FIELD_TRIALS.md and docs/v2/ROADMAP.md. Framework identity remains 2.0.0-preview.5; the existing immutable preview tag is retained. Stable release promotion remains subject to the documented field, migration and final release checks.