Remove gh-workflow legacy archive config fallbacks

Context

Epic #11187 Phase 6 is rescuing the resources/content archive substrate from stale issue-archive / pr-archive / unversioned assumptions. Discussion #11359 and PR #11362 narrow the immediate data cleanup, but live V-B-A on the gh-workflow config surface shows a separate contract pocket still outside #11360 / #11362 scope.

Current branch evidence:

• ai/mcp/server/github-workflow/config.mjs still exposes issueSync.archiveDir pointing at resources/content/issue-archive.
• ai/mcp/server/github-workflow/config.template.mjs exposes the same legacy archiveDir fallback.
• Both config files still expose defaultArchiveVersion: 'unversioned'.
• Consumer grep still finds issueSync.archiveDir references in IssueSyncer.mjs, LocalFileService.mjs, and related unit tests.

This is a config-contract cleanup ticket, not another data-migration ticket. The goal is to prevent the deleted legacy folders and the invalid unversioned bucket from remaining alive as official gh-workflow configuration.

Problem

archiveRoot is the intended versioned archive root. Keeping archiveDir and defaultArchiveVersion in the public config/template layer creates three risks:

1. Fresh worktrees copy stale contract defaults from config.template.mjs.
2. Consumers and tests keep treating resources/content/issue-archive as a supported path after Phase 6 removes the folder.
3. unversioned remains a config-supported archive bucket even though the archive structure must use real release versions only.

Acceptance Criteria

• ai/mcp/server/github-workflow/config.mjs no longer exposes issueSync.archiveDir or issueSync.defaultArchiveVersion as part of the public gh-workflow config contract.
• ai/mcp/server/github-workflow/config.template.mjs is kept in sync with config.mjs and no longer seeds archiveDir or defaultArchiveVersion into fresh clones/worktrees.
• Every live consumer of issueSync.archiveDir is audited. Consumers are either removed, rewritten to derive from archiveRoot, or given a narrowly documented transitional fallback that does not require resources/content/issue-archive to exist at boot.
• Unit tests and config-completeness checks are updated so they no longer require archiveDir or defaultArchiveVersion as mandatory config keys.
• rg "defaultArchiveVersion|issueSync\.archiveDir|resources/content/issue-archive|unversioned" ai/mcp/server/github-workflow ai/services/github-workflow test/playwright/unit/ai/services/github-workflow -g "*.mjs" shows no active config-contract fallback. Historical comments or tests may remain only when they describe the retired behavior and cannot steer runtime paths.
• gh-workflow boot or the nearest available config/unit validation passes after PR #11362 lands, with no ENOENT path dependency on resources/content/issue-archive.

Out of Scope

• PR #11362 data cleanup and manifest-generation fixes.
• MetadataManager / PullRequestSyncer archiveVersion propagation cleanup; that is Pocket B and should be handled by a separate ticket.
• Recursive archive ingestion for IssueIngestor / graph sources; that is already tracked by #11361.
• Release publishing mechanics in buildScripts/release/publish.mjs unless a direct config consumer is discovered.

Avoided Traps

• Do not bundle this into #11360 / #11362; those already have enough blast radius.
• Do not keep archiveDir for backward compatibility without a measured sunset condition.
• Do not treat unversioned as a release version.
• Do not remove consumer code blindly; first prove whether it is runtime contract, historical fallback, or test-only scaffolding.

Related

• Parent epic: #11187
• Rescue strategy: Discussion #11359
• Immediate cleanup ticket: #11360
• Current cleanup PR: #11362
• Existing archive-ingestion follow-up: #11361
• Historical config completeness context: #10209

Origin Session

• Origin Session ID: d6d89930-f408-42a0-b60e-ec4487a8cc46

Retrieval Hint

Search for archiveDir defaultArchiveVersion unversioned gh-workflow config Phase 6.