fix: let PipelineBoard card content form its own accessible name

[smartcalsystems-sketch]

Problem

Each pipeline card's <Link> has aria-label={${title}, ${reward}}, which overrides the link's visible content for assistive tech. The org/repo #N line — the main way a maintainer identifies which issue a card is — is never announced; only the title and reward the aria-label spells out manually are.

Fix

Dropped the aria-label so the link's accessible name is computed from its actual visible content instead (the org/repo #N line, the title, and the formatted reward are all already rendered inside it) — nothing is lost, the repo reference is gained.

Note for maintainers: the issue mentions this is the same pattern used in BountyCard.tsx, and that's still accurate — I left it untouched since it's a separate component outside this issue's scope, but it likely wants the identical fix in a follow-up.

Testing

• Added a test asserting the card link's accessible name includes the org/repo/issue reference, the title, and the reward — not just the two the old aria-label provided.
• Full PipelineBoard.test.tsx suite: 8/8 passing (7 pre-existing + 1 new), zero regressions.
• tsc --noEmit and eslint clean on both changed files.

Closes #694

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