feat(skills): size limits for agent writes + fuzzy matching for patch (#4414)

* feat(skills): add content size limits for agent-created skills

Agent writes via skill_manage (create/edit/patch/write_file) are now
constrained to prevent unbounded growth:

- SKILL.md and supporting files: 100,000 character limit
- Supporting files: additional 1 MiB byte limit
- Patches on oversized hand-placed skills that reduce the size are
  allowed (shrink path), but patches that grow beyond the limit are
  rejected

Hand-placed skills and hub-installed skills have NO hard limit —
they load and function normally regardless of size. Hub installs
get a warning in the log if SKILL.md exceeds 100k chars.

This mirrors the memory system's char_limit pattern. Without this,
the agent auto-grows skills indefinitely through iterative patches
(hermes-agent-dev reached 197k chars / 72k tokens — 40x larger than
the largest skill in the entire skills.sh ecosystem).

Constants: MAX_SKILL_CONTENT_CHARS (100k), MAX_SKILL_FILE_BYTES (1MiB)
Tests: 14 new tests covering all write paths and edge cases

* feat(skills): add fuzzy matching to skill patch

_patch_skill now uses the same 8-strategy fuzzy matching engine
(tools/fuzzy_match.py) as the file patch tool. Handles whitespace
normalization, indentation differences, escape sequences, and
block-anchor matching. Eliminates exact-match failures when agents
patch skills with minor formatting mismatches.

tools/skills_hub.py

@@ -2525,6 +2525,22 @@ def install_from_quarantine(
     if install_dir.exists():
         shutil.rmtree(install_dir)
 
+    # Warn (but don't block) if SKILL.md is very large
+    skill_md = quarantine_path / "SKILL.md"
+    if skill_md.exists():
+        try:
+            skill_size = skill_md.stat().st_size
+            if skill_size > 100_000:
+                logger.warning(
+                    "Skill '%s' has a large SKILL.md (%s chars). "
+                    "Large skills consume significant context when loaded. "
+                    "Consider asking the author to split it into smaller files.",
+                    safe_skill_name,
+                    f"{skill_size:,}",
+                )
+        except OSError:
+            pass
+
     install_dir.parent.mkdir(parents=True, exist_ok=True)
     shutil.move(str(quarantine_path), str(install_dir))