fix: preserve non-ASCII (CJK) path segments in auto-generated project name

[mvanhorn]

What does this PR do?

Fixes #571: cbm_project_name_from_path() derived an auto project slug by mapping
every byte outside [A-Za-z0-9._-] to - and then collapsing dashes. For a path
such as /Users/yunxin/Desktop/开发/后端, every UTF-8 byte of the CJK segments is
unsafe, so each segment collapsed to a single - that was then trimmed away,
yielding Users-yunxin-Desktop. Two different non-ASCII directories under the same
ASCII parent collapsed to the same name, so the identifying information was
silently lost and distinct repos collided. Users with non-Latin directory names
saw indexing create a DB under a truncated, unrecognizable name.

This change percent-encodes non-ASCII bytes instead of discarding them, so
non-ASCII paths keep a distinct, recoverable name. It also keeps the slug
generator in agreement with cbm_validate_project_name() -- the same invariant
that motivated the #349 space fix (a name that indexes but resolve_store
later rejects reports project-not-found).

Changes:

• src/pipeline/fqn.c -- cbm_project_name_from_path() now percent-encodes any
  byte >= 0x80 as uppercase %HH into a new, larger buffer, while ASCII
  separators / unsafe bytes still map to -. ASCII slugs are byte-identical to
  before (e.g. /home/u/my project -> home-u-my-project). The existing
  dash/dot collapse and leading/trailing trim are preserved. Because the slug is
  later used as <cache>/<name>.db, long slugs are bounded to 200 bytes with a
  deterministic FNV-1a hash suffix so distinct long paths still produce distinct
  names and stay within the OS filename-component limit. Includes overflow guards
  and correct memory management.
• src/foundation/str_util.c -- cbm_validate_project_name() additionally
  accepts %. It remains filesystem-safe; the existing .., /, \, and
  leading-. rejections are unchanged.
• tests/test_fqn.c -- new coverage for CJK percent-encoding, distinctness, the
  long-path bound, the %-accepting validator, and an unchanged-ASCII
  regression.

Example: /Users/yunxin/Desktop/开发/后端 now yields
Users-yunxin-Desktop-%E5%BC%80%E5%8F%91-%E5%90%8E%E7%AB%AF (distinct, valid)
instead of Users-yunxin-Desktop.

Checklist

• Every commit is signed off (git commit -s) -- required, CI rejects
  unsigned commits (DCO, see CONTRIBUTING.md)
• Tests pass locally (make -f Makefile.cbm test) -- 5689 passed, 0 failed
• Lint passes (make -f Makefile.cbm lint-ci) -- clang-format clean on
  touched files
• New behavior is covered by a test (reproduce-first for bug fixes)

Fixes #571