chore: remove dead code, fix dream archive status, and update docs

[parlakisik]

Summary

A dead-code sweep over the root module and tools/ctxctl, plus two fixes it surfaced.

How candidates were found: golang.org/x/tools/cmd/deadcode over ./... ./tools/ctxctl/..., with and without -test, intersected across GOOS darwin/linux/windows. 49 functions came up that the shipped binaries never reach (the kb writer stack was excluded on purpose). Each candidate was checked against specs/, .context/TASKS.md, git history, and whether it serves as a test seam. Anything uncertain was kept.

1. chore: remove dead code and update docs

• Removed: internal/cli/initialize/core/vscode and internal/write/vscode. ctx init never called them; .vscode/mcp.json ships through ctx setup copilot and cline. The text keys and config/vscode constants only they used are also gone.
• Removed: dream SourceStatusKnown, DecisionKnown, errDream.ReadSource, and the constants only they used.
• Removed: pad blob.Contains; parse.FormatEntries, replaced earlier by FormatEntriesWithIDs; and store.EnsureGitignore, replaced by project.EnsureGitignoreEntries.
• Removed: the rc.ArchiveAfterDays() getter. The .ctxrc field stays so existing configs still parse, and it is now documented as inert (docs, schema, .ctxrc.dev).
• Moved into _test.go: parser.find, parser.registeredTools, and the hooks registry helpers.
• Kept on purpose:
  • hub cluster-mode scaffold (tasks H-02, H-13, H-14)
  • disclosure invariant checks (pd-m1 plan and compliance test)
  • closeout Write (kb pipeline spec)
  • dream.Backup (backup-before-mutate in the spec)
  • ParseFile
  • the kb writer stack
  • test seams (rc.Reset, SetSink, SetDirForTest, testctx.Declare, and similar)
• Docs: package doc.go files, docs/ configuration and CLI reference, .context notes. The three site/ pages were regenerated with the pinned zensical 0.0.51; unrelated generator churn was reverted.

2. test(codex): stop deriving paths from env in deploy tests

golangci-lint 2.14's gosec G703 flags os.Getenv-derived paths in deploy_test.go; this already fails on main with 2.14. withTempProjectAndHome now returns the temp $CODEX_HOME, so fixtures use a t.TempDir path.

3. fix(dream): record archived status in state.json on archive

specs/ctx-dream.md requires per-source status to track dispositions, but only active was ever written. An archive moved the idea into ideas/done/ while state.json still said active. The archived source's record now becomes archived. Covered by the new test TestAcceptArchiveMarksSourceArchived.

Test plan

• go build / go vet on ./... ./tools/ctxctl/... (Go 1.27.1)
• go test ./... ./tools/ctxctl/...: all packages pass, including TestNoDeadExports
• golangci-lint 2.14.0: 0 issues
• shellcheck, lint-drift, lint-docstrings, lint-mixed-funcs, lint-imports (advisory notes only, in untouched files)
• version, Go version, why-docs, copilot/codex/opencode/pi skills, and steering sync checks
• deadcode re-run: the only remaining entries are deliberately kept symbols and the kb stack