feat(linear): support repo-scoped credentials

[camwest]

Summary

Support repo-scoped Linear credentials so different repos can bind to different Linear accounts/workspaces.

This enables setups like:

• repo-a -> Linear account/workspace A
• repo-b -> Linear account/workspace B

What changed

• Added auth_scope to repo links and migration support.
• Added scoped credential storage helpers using linear:<scope> service keys.
• Updated Linear link flow to:
  • persist scoped credentials per repo/account/workspace,
  • support -o reauth,
  • retry OAuth once when requested -o team=... is not in the current auth context.
• Updated Linear forge resolution and token refresh to read/write scoped credentials when auth_scope is present.
• Updated logout behavior so isq logout linear clears both global and scoped Linear credentials.
• Updated auth detection (status/doctor) to recognize scoped credentials.
• Updated docs:
  • README.md
  • skills/isq/SKILL.md
  • CHANGELOG.md

Key files

• src/db/schema.rs
• src/db/repos/links.rs
• src/forges/linear/link.rs
• src/forges/linear/mod.rs
• src/forges/linear/auth.rs
• src/forges/forge_type.rs
• src/cli/link.rs
• src/forges/auth.rs
• src/cli/doctor/checks.rs

Validation

• cargo fmt
• cargo test (202 passed)

Notes

• Existing Linear-linked repos created before this change should run isq link linear -o team=<TEAM> once to persist auth_scope.

[camwest]

• feat(linear): support repo-scoped credentials #163 👈 (View in Graphite)
• master

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