fix: use GitHub merge state to fix misleading Mergeable classification

[ibetitsmike]

Summary

PRs blocked by required reviews were incorrectly classified as Mergeable when checks passed. Now uses GitHub's mergeStateStatus field as the source of truth.

Changes

Rust backend (src-tauri/src/):

• models.rs — Added merge_state_status: Option<String>
• github.rs — Extended GraphQL fragment to fetch mergeStateStatus; idiomatic str::to_owned
• menu.rs — Added is_actually_mergeable() helper; Mergeable filter uses merge state + excludes pending/failed checks; 8 unit tests with exclusivity assertions

Svelte frontend (src/lib/):

• types.ts — Added MergeStateStatus literal union type; updated PullRequest field
• stores.ts — Added isActuallyMergeable() and isCheckFailed() helpers; Mergeable filter uses merge state + excludes pending/failed checks
• components.test.ts — 8 grouping tests with exclusivity assertions + review-requested boundary test

Verification

• npm run test ✅ (29 passed)
• npm run check ✅ (0 errors, 0 warnings)
• npm run smoke ✅
• cargo test / cargo check ✅
• Codex Review ✅

[chatgpt-codex-connector]

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Reviewed commit: 90ed561aa7

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[ibetitsmike]

@codex review

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Reviewed commit: 90ed561aa7

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[ibetitsmike]

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

ℹ️ About Codex in GitHub

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