[fas89]

Moves the pin from forge-cli v0.21.0 to v0.27.0 (peeled c0e97c076f735205f4767f67f0bd05bcd78a47cd). 0.7.6 has been the stable schema there since 0.26.0, and 0.7.7 is the preview.

What changes

• Schemas. 0.7.2–0.7.5 are byte-identical to the copies here and stay as they are. fluid-schema-0.7.6.json is replaced and fluid-schema-0.7.7.json added, both byte for byte from the tag. scripts/schema-versions.json: latestStable 0.7.6, preview ["0.7.7"], synced through 0.7.7.
• Generated output. specs/0.7.6, specs/0.7.7 and schema-diffs/ (including the new diff-0.7.6-to-0.7.7) come from the locked renderer.
• Corpus, 0.7.6. tests/0.7.6/trigger-continuous.json pins trigger.type: continuous (forge-cli #734): it is refused beside cron, schedule, datasets, event and timetable, and a non-object trigger gets exactly one error. tests/0.7.6/bitol-fields.json pins the Bitol-shaped fields 0.7.6 gained after v0.21.0. Descriptions lose the word "preview".
• Corpus, 0.7.7. tests/0.7.7/ and tests/optional/0.7.7/ start from the 0.7.6 corpus. Three groups are added: stream-source, record-mapping and nested-columns.
• tests/meta_test.py. The stray-schema fixture used 0.7.7, which is now synced, so it uses 0.7.8. The gate is unchanged.
• Docs. docs/releases/0.7.6.md becomes the stable page. docs/releases/0.7.7.md is new. docs/schema/changelog.md and every status line now say 0.7.6 stable and 0.7.7 preview.

Gates (all exit 0)

Gate	Result
tests/meta_test.py	50/50
conformance/run.py	1958 cases pass
conformance/mutation_coverage.py --min-coverage 40	0.7.5 41.0%; 0.7.6 45.7% (41.7% without the new cases); 0.7.7 48.2% (39.7% without)
conformance/check_reference.py against data-product-forge 0.27.0	1958 cases, 0 disagree; the same 6 optional format cases as before are not implemented
scripts/check-compat.py	0.7.6 to 0.7.7: 0 breaking, 2 additive
scripts/check-schema-drift.py	every synced schema matches v0.27.0
generate-docs.py --check, generate-schema-diffs.py --check	clean
npm run docs:build	clean

For the maintainer

1. A rule outside the schema. fluid validate 0.27.0 refuses a map column whose key is not a required string ("supported map keys are required strings"), but the 0.7.7 schema accepts one. The valid map cases here declare required: true, so both agree, and 0.7.7.md notes the rule as non-normative. Keep it that way, add an optional-tier case, or raise it upstream?
2. Depth of the 0.7.6 promotion. Status text, the quickstart, the minimal contract and the cheatsheet rows moved to 0.7.6. These still use 0.7.5, which 0.7.6 still accepts: the specification.md section 1 tables, the anatomy.md YAML blocks and examples 1–13. A rewrite against 0.7.6 would be a separate pass, like docs: state 0.7.5 stable and 0.7.6 preview, rewrite the specification against 0.7.5, and make every example validate #51.
3. package.json says 0.7.5 and package-lock.json 0.7.4. Neither is touched here.