[Bugfix #749][Bugfix #750] Fix Gitea forge crash and field normalization

[waleedkadous]

Summary

Two tightly-coupled Gitea-forge regressions reported in v3.0.3 against a Forgejo instance, fixed together since the second was masked by the first (Tower 500'd before the rendering bug was visible).

#749 — labels.map is not a function 500 on Tower overview

Forgejo/Gitea returns labels: "" (or null) for unlabeled issues, where GitHub always returns []. parseLabelDefaults() in lib/github.ts called .map() unconditionally and crashed.

• Coerce non-array inputs to [] before mapping: Array.isArray(labels) ? labels.map(...) : []
• Widen the parameter type to Array<{name}> | null | undefined | string to reflect the actual cross-forge runtime shape (the project's forge-contracts already document presets as "best-effort" with non-conforming shapes treated as nulls; this lifts the contract into the type system at one call site)
• Regression tests for empty-string, null, and undefined paths alongside the existing array (GitHub) path

#750 — #undefined / NaNd in Tower overview for Gitea

Once the 500 was patched, every backlog row rendered #undefined and ages showed NaNd because the Gitea preset scripts piped raw tea --output json straight to the overview, which expects the GitHub-compatible shape declared in forge-contracts.ts.

Each of the four affected scripts now requests an explicit --fields list and normalizes via jq:

tea field	normalized to
index (string)	number (int)
created	createdAt
author (flat string)	author.login
labels (CSV string or "")	labels[].name
assignees (CSV string or "")	assignees[].login
description	body

• recently-closed.sh: maps updated → closedAt (Gitea has no closed_at field on list output; for issues edited after close this overestimates, acceptable for the 24h overview window)
• recently-merged.sh: filters select(.merged == true) (same predicate scripts/forge/gitea/pr-exists.sh already uses) and maps updated → mergedAt, head.ref → headRefName

jq is already a runtime dependency of the gitea preset (pr-exists.sh, user-identity.sh both use it) so this introduces no new tooling requirement.

Test plan

• Run unit tests — pnpm exec vitest run src/__tests__/github.test.ts → 55/55 pass (4 new regression cases)
• Typecheck — pnpm exec tsc --noEmit clean
• Validate jq filters offline with synthetic tea-shaped fixtures (empty-string labels, CSV labels, merged-vs-closed PRs) — output matches IssueListItem / PrListItem shapes in forge-contracts.ts
• Forgejo round-trip — verified by report reproducer; requires the original reporter or a Gitea instance for end-to-end Tower overview check
• CMAP review (will run next)

Fixes #749
Fixes #750