Extract sigil-lang: rewire monorepo consumers from-git

Drops packages/sigil-lib/ + packages/sigil-stdlib/ from the monorepo workspace; pins both packages of the new two-package standalone repo codeberg:sigil/sigil-lang from every monorepo consumer that used from-workspace:

  (from-git url: "codeberg:sigil/sigil-lang"
            package: "sigil-lib"     version: "^0.13.1")
  (from-git url: "codeberg:sigil/sigil-lang"
            package: "sigil-stdlib"  version: "^0.13.1")

Per the architectural pivot in design/sigil-versioning-and-distribution (2026-04-25 evening): sigil-cli stays in codeberg:sigil/sigil forever; the language implementation (VM + stdlib + compiler source) moves to the new codeberg:sigil/sigil-lang repo. Decision per the brief recommendation: REMOVE the duplicate sigil-lib + sigil-stdlib from the monorepo (Phase 8 sweep is mechanical; prefer fail-loud over silently working through the duplicate).

Rewire scope:

• 12 monorepo packages declared from-workspace on sigil-lib or sigil-stdlib. All swapped to from-git pins: sigil-cli, sigil-args, sigil-ansi, sigil-docs, sigil-git, sigil-socket, sigil-build, sigil-version, sigil-run, sigil-web-run.
• sigil-run + sigil-web-run additionally got the §6a fix: hardcoded ../sigil-lib/include + ../sigil-lib/src dropped from compile-c-sources include-dirs:; flags: wrapped in (with-sigil-c-flags ...) so sigil-build's auto-inject supplies the paths from the from-git resolved sigil-lib.
• Root package.sgl drops sigil-lib + sigil-stdlib from the workspace packages list.
• Root dev-redirects.sgl adds codeberg:sigil/sigil-lang → ../task-extract-sigil-lang/sigil-lang (canonical relative path from monorepo root).
• Makefile points LIBSIGIL_DIR + STDLIB_PKG at .sigil/deps/<name>; preflight $(error ...) refuses to run if those symlinks aren't resolved; gc-stress + native-test paths follow.
• packages/sigil-lib/ + packages/sigil-stdlib/ deleted (~80 files).

Validation:

• make test-scheme: 154/154 passed
• sigil test --redirects (workspace discovery + dev binary): 1035 passed / 2 failed. The 2 failures (test-mcp-tools, test-mcp-nrepl-tools) are pre-existing latent bugs from the sigil-mcp §6b split — namespaces in cli/mcp/{tools,nrepl}.sgl weren't renamed per §6b step 5; master masks the bug via stale build/dev cache (.sgb timestamps from pre-split). Surfaces on my clean rebuild. Out of scope to fix here.
• sigil-stdlib direct tests (688 passed / 0 failed) confirm the ~1000-test count drop is workspace-discovery only — same pattern as sigil-test extraction.
• Bootstrap via Make clean. --version, eval (string-upcase) green.

The monorepo continues to work as the user-facing sigil-cli source. Next phases (per design doc): cross-repo sigil: sweep (Phase 8), sigil-build extraction (Phase 9), sigil-git/socket extraction (Phase 10), 0.14.0 coordinated release (Phase 11).