fix(deploy): #27 - the managed .gitignore block ignores .venv as a file, directory or link

Both installers wrote `/.venv/`, which only matches a directory: a .venv
symlink (the worktree recipe links the control root's) or file showed up as
untracked in installed repositories. The managed block now has `/.venv`.
Existing installations get it on the next install/update, which rewrites the
block between its markers as a whole; the integrity values are unaffected
(.gitignore is in neither asset_hashes.txt nor the install manifest).

Tests W10 (both installers; .venv as link, file and directory all ignored) and
W11 (a pre-#27 block is replaced, user lines outside it are kept, .gitignore
stays out of the ledgers).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017R3Eg7MEpSWnm1oB9ZPP6G

deploy/install.sh

@@ -546,7 +546,7 @@ gi_path, start_marker, end_marker = sys.argv[1], sys.argv[2], sys.argv[3]
 
 block_lines = [
     start_marker + "\n",
-    "/.venv/\n",
+    "/.venv\n",
     "/.mam/\n",
     "/.mam_deploy/\n",
     "/.mam.env\n",

deploy/install_mam.sh

@@ -246,7 +246,7 @@ gi_path, start_marker, end_marker = sys.argv[1], sys.argv[2], sys.argv[3]
 
 block_lines = [
     start_marker + "\n",
-    "/.venv/\n",
+    "/.venv\n",
     "/.mam/\n",
     "/.mam_deploy/\n",
     "/.mam.env\n",