GitHub mirror repo inference should parse Markdown Source links

[miyaontherelay]

Problem

Factory has fallback logic to infer a GitHub mirror's source repo from the Linear issue description when labels are missing. It currently handles plain source lines like:

Source: https://github.com/AgentWorkforce/relayfile-adapters/issues/224

But it does not handle Markdown link forms like:

Source: [https://github.com/AgentWorkforce/relayfile-adapters/issues/224](<https://github.com/AgentWorkforce/relayfile-adapters/issues/224>)

Observed with Linear AR-311, mirrored from AgentWorkforce/relayfile-adapters#224: factory triage AR-311 routed to factory via repos.default instead of relayfile-adapters because the mirror did not have the repo label and the Markdown Source fallback failed.

Expected

githubMirrorRepoForIssue() / source URL parsing should accept:

• plain GitHub issue URLs
• Markdown link syntax [text](url)
• autolinks wrapped in <...>
• structured source.url when present

Acceptance criteria

• Label-less GitHub mirror issues route to the configured repo using Markdown Source links.
• Regression test uses the exact Source: [https://...](<https://...>) shape.
• If both structured source and description source exist, structured source remains preferred.

Related

• Source issue: GitHub: export shared mount-path parser for issues and PRs relayfile-adapters#224
• Repro Linear mirror: AR-311

[miyaontherelay]

Related startup/backfill issue: #32. Related Linear label preservation issue: AgentWorkforce/relayfile-adapters#226.

[miyaontherelay]

Factory-side requirement from the GitHub mirror repro: factory should own deriving the repo routing label from the GitHub source issue before creating the Linear mirror.

Example: when mirroring AgentWorkforce/relayfile-adapters#224, factory should include the configured relayfile-adapters routing label in the Linear create payload, even if the GitHub issue only has the factory trigger label.

That keeps routing policy in factory. relayfile-adapters should only be responsible for applying the labels supplied in the writeback payload, or surfacing a clear error/dead-letter if they cannot be applied.