feat: path budget - a file's path stays at 160 characters or fewer; new, rename, move and raw accept refuse more, lint reports Long Paths (#163)

Files changed:
- CHANGES.md
- README.md
- VERSION
- instructions/page-lifecycle.md
- kb/CONTRACT.md
- tools/CONTRACT.md
- tools/chemenu/commands/_util.py
- tools/chemenu/commands/lint.py
- tools/chemenu/commands/new_page.py
- tools/chemenu/commands/page_ops.py
- tools/chemenu/commands/raw_cmd.py
- tools/chemenu/lint_core.py
- tools/chemenu/tests/test_lint.py
- tools/chemenu/tests/test_new_page.py
- tools/chemenu/tests/test_page_ops.py
- tools/chemenu/tests/test_raw_cmd.py
- tools/chemenu/tests/test_titles.py
- tools/chemenu/titles.py

kb/CONTRACT.md

@@ -138,6 +138,20 @@ writes to; `rename` only for `--to`, so a page that already breaks the rule can
 away from it), and never write over an existing file. `wikitool lint` reports existing pages that
 break the rule as Unportable Titles, a hard error at every `kb_version`.
 
+**A path has a budget too.** Windows counts 259 characters for a whole path, the folder the
+instance is checked out into included, and long paths are off on the target system. The path of
+any file below the instance root - `kb/` page or `raw/` source - therefore stays at **160
+characters or fewer**, written with `/` and counted in UTF-16 code units, which is how Windows
+counts: an emoji outside the Basic Multilingual Plane takes two. The folder limit that `doctor`
+checks is the other half of the same sum.
+
+`wikitool new` (every root), `wikitool rename` (`--to` only, also under `--dry-run`), `wikitool
+move` (a single page, and `--reconcile`, which skips and names such a target) and `wikitool raw
+accept` (the target under `raw/`; the remedy is renaming the file in `incoming/`) refuse a path
+over the budget before writing anything. `wikitool lint` reports existing files over it as Long
+Paths - advisory, not a hard error, so a corpus that predates the budget still passes
+`--fail-on-error`; the fix is `wikitool rename`.
+
 ## Every page should
 
 - [ ] Carry a clear, descriptive title and a summary near the top