fix(kb-lint): a markdown link may not resolve into the quarantine

The link-integrity pass ended in `is_file()`, and `.AGENTTRASH/` is a real directory on
this machine: a page pointing at `[x](.AGENTTRASH/gone.md)` passed the gate here and was a
dead link everywhere else, because the quarantine is gitignored. This is incident #57 — the
wikilink resolver resolving `[[log]]` onto a quarantined copy — reproduced in markdown
clothing, which is to say: fixing one resolver while leaving the identical assumption in the
other one is not a fix.

A link that lands inside the bundle must land on a page that belongs to the bundle. A link
that leaves the bundle is still honoured (`tools/live-sync.md` -> `../../AGENTS.md` points at
the operating contract, which is not bundle content and is real on disk). Red test added
first, both link spellings covered; nothing previously green changed.

Refs #64

scripts/kb-lint.sh

@@ -23,6 +23,7 @@ def pages():
 # Names that a wikilink may point at: exactly the pages pages() reports. Deriving this
 # once keeps linting and link resolution from disagreeing about what exists.
 live = {p.stem for p in pages()}
+live_paths = {p.resolve() for p in pages()}
 
 for p in pages():
     rel = p.relative_to(kb)
@@ -70,8 +71,16 @@ for p in pages():
     text = re.sub(r"^```[^\n]*$^```[^\n]*$", "", p.read_text(errors="replace"), flags=re.M)
     rel = p.relative_to(kb)
     for m in re.finditer(r"\]\((?!https?:|#)([^)#\s]+\.md)", text):
-        target = (p.parent / m.group(1)).resolve() if not m.group(1).startswith("/") else (kb / m.group(1).lstrip("/"))
-        if not Path(target).is_file():
+        target = (p.parent / m.group(1)).resolve() if not m.group(1).startswith("/") else (kb / m.group(1).lstrip("/")).resolve()
+        # A link INSIDE the bundle must land on a page that belongs to the bundle: `is_file()`
+        # alone also accepted a target parked in .AGENTTRASH/, which is gitignored — green here,
+        # a dead link on every machine that pulls (#57 again, in markdown clothing). A link that
+        # leaves the bundle is allowed: ../../AGENTS.md is the operating contract, not bundle
+        # content, and it is real on disk.
+        if kb in target.parents:
+            if target not in live_paths:
+                violations.append(f"{rel}: broken relative link -> {m.group(1)}")
+        elif not target.is_file():
             violations.append(f"{rel}: broken relative link -> {m.group(1)}")
     for m in re.finditer(r"\[\[([^\]|#]+)", text):
         # wikilinks resolve by filename anywhere in the KB (Obsidian semantics) — but only