Add GitHub PR write actions to the Inbox

[viannaanalyst]

What

Adds GitHub pull request write actions to the Inbox, on top of the existing read/review surfaces.

• Merge — split button with squash (primary) / merge commit / rebase, "delete branch after merge" option, and native confirmation that names the method and deletion.
• Review submission — pending review: inline comments on the Code-tab diff accumulate in a review bar, then publish as one GraphQL addPullRequestReview call with Comment / Approve / Request changes. Request changes requires a review body; approve is disabled on your own PR.
• Close / reopen and label / assignee / reviewer editing with searchable multi-select popovers.
• Gating — merge disabled with a reason for closed/draft/conflicting/blocked PRs; self-approve, empty review payloads, and invalid merge methods are rejected before gh runs.
• i18n — pt-BR entries for every new string.

Rust commands wrap the authenticated gh CLI (existing patterns); no new dependencies and no new auth path.

Implementation notes

• GitHubWorkItemDetails gains id, state, isDraft, mergeable, mergeStateStatus, labels, assignees, reviewRequests (all optional to keep tracker details typechecking); GithubPrDetails is the required shape for PR actions.
• Pending review drafts persist per cwd:number for the session; the review bar is keyed to reset its dialog after a successful publish.
• Inline comments reuse the existing per-line affordance in UnifiedDiffView, redirected from chat to the pending review via a new onLineComment prop. Default behavior is unchanged when the prop is absent.
• gh pr merge / close / reopen / edit are silent on success, so those calls allow empty stdout while still surfacing failures.

Tests

• Web: npm run check:web — 226 files / 2379 tests passed, tsc --noEmit clean.
• Rust: npm run check:rust — fmt clean, clippy -D warnings clean, 310 tests passed.
• New coverage: prReview.test.ts (draft, gating, persistence), PrReviewBar.test.ts (bar + inline edit + request handling), PrActions.test.ts (gating, merged state), githubPrWrite.test.ts (invoke payloads), Rust pr_merge_args / pr_edit_flags / pr_state_args / pr_review_payload tests.

Pending before merge

• Manual end-to-end on a scratch PR with a second reviewer account: each merge method, approve/request changes, close/reopen, metadata edits, inline comments on added/context/deleted lines, and a blocked merge error.