fix(nix): keep docs and CI out of the derivation sources

[colonelpanic8]

Problem

nix/package.nix and nix/desktop-package.nix both take the whole repository
as src and exclude only a handful of paths. That leaves docs/, .github/,
docker/, the agent/editor config directories and the top-level markdown as
build inputs of both derivations.

None of them reach the build, but any one of them changing produces a new
derivation and therefore a full rebuild — including the Expo web export, which
dominates the build — to arrive at a byte-identical result. A docs-only or
workflow-only commit currently costs a complete desktop rebuild.

The npmDeps coupling

Tightening the desktop filter alone does nothing, which is worth spelling out:
desktop-package.nix inherits npmDeps from the daemon, so the daemon's src
feeds the desktop derivation too. With only the desktop filter changed, a
docs-only edit still produced a new npm-deps derivation, hence a new desktop
derivation, hence a full rebuild. Both filters have to move together.

Markdown scope

Markdown is excluded at the top level only (README, CHANGELOG, AGENTS...).
skills/*/SKILL.md is a runtime file both derivations copy into their output,
so a repository-wide *.md exclusion would silently ship empty skill
directories — the derivation hash test would not have caught that.

Verification

• nix eval .#desktop.drvPath and .#paseo.drvPath are now unchanged across
  edits to docs/, .github/workflows/, docker/ and README.md; before this
  change both paths moved.
• nix build .#desktop succeeds, and the output still contains all 5
  skills/*/SKILL.md files, with no docs/ or .github/ in the result.

[greptile-apps]

Greptile Summary

Tightens both Nix source filters to prevent documentation and CI-only changes from invalidating daemon and desktop derivations.

• Excludes documentation, workflow, Docker, and agent/editor configuration directories.
• Excludes only top-level Markdown while preserving runtime Markdown under skills/.
• Applies matching exclusions to the daemon source that supplies the desktop package’s npmDeps.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
nix/desktop-package.nix	Excludes non-build inputs from the desktop source without removing nested runtime Markdown.
nix/package.nix	Applies equivalent filtering to the daemon source so inherited desktop npm dependencies remain stable.

_{Reviews (2): Last reviewed commit: "fix(nix): keep docs and CI out of the de..." | Re-trigger Greptile}