feat(v4.0.0): word-level access control at the prompt, as v3

- Each entry's flags cell also holds v3's four fields: denied, pinned,
  mode and a 16-bit TTL.
- compile.v4: INTERPRET checks every word it is about to execute or
  compile -- recheck at TTL 0, else count down; a denied word is refused
  with v3's line, the stack emptied and the line ended.
- capsule/acl.v4: ACL-MODE@ ACL-MODE! ACL-TTL@ ACL-TTL! ACL-ALLOW@
  ACL-ALLOW! ACL-PINNED? ACL-PIN ACL-INHERIT ACL-INIT-PRIMITIVES ACL-HEAT@
  ACL-WORD-ID, and ACL-HOOK.
- capsule/ACL.fth: v3's ACL.4th as FORTH source the node compiles; loading
  it switches access control on.
- v3 checks every execution, inside definitions too.  v4's code is native,
  so it checks a word when it is compiled as well as when interpreted; a
  call compiled while the word was allowed is not checked again.
  DECOMPOSITION.md 5.20 says so.
- ACL-HEAT@ is 0 until heat is readable (D-6).
- tests/test_host_quit.c: seven transcripts of the v3 binary; the policy
  file loaded and exercised; COLD.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/capsule/core.v4

@@ -17,7 +17,7 @@
 \    9 Shift count out of range      10 Protected word
 \   11 Division by zero (Q./)        12 Argument out of range
 \   13 Block out of range            14 No block is being loaded
-\   15 Deferred word not set
+\   15 Deferred word not set         16 Not a word
 \   -1 the word has printed its own message
 
 macro SWAP   over push push drop pop pop   endmacro