chore(ci): update workflow path triggers and improve docs build

[sakinaroufid]

Description

Improves existing CI workflows:

linter.yaml:

• Adds paths filter so the linter workflow only triggers on relevant file changes instead of every PR
• Reformats FILTER_REGEX_EXCLUDE to multiline YAML for readability

docs.yml:

• Updates path trigger from requirements-docs.txt to pyproject.toml + uv.lock
• Changes uv sync to uv sync --all-groups to install all dependency groups
• Adds explicit Rust toolchain (dtolnay/rust-toolchain@stable) and cargo caching (Swatinem/rust-cache@v2) before the existing cargo install ucp-schema step

Other:

• Adds EDITMSG to .cspell/custom-words.txt
• Minor comment reordering in .pre-commit-config.yaml (prettier hook)

This is part 3 of 3 from #13, split per maintainer request.

Type of change

• New feature (non-breaking change which adds functionality)

---

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

[sakinaroufid]

@nearlyforget pinging you here!