fix: A1-10 write template file to disk on create instead of leaving file_path empty

SPECGAPS.md

@@ -19,7 +19,7 @@ Gap categories: **SC** = spec correct, fix code | **CS** = code correct, update
 | A1-7 | ~~Template lookup must use all 4 levels (post→tag→category→default)~~ | template_context.allium:267-277 | `resolve_post_template_slug/3` implements tag→category cascade; all callers (preview, generation) updated | **Resolved:** `resolve_post_template_slug/3` in template_selection.ex, callers in preview.ex, router.ex, outputs.ex updated, 8 tests added |
 | A1-8 | ~~`ValidateLiquid`/`ValidateScript` before publish~~ | template.allium:110, script.allium:165 | `publish_template` validates Liquid via `Liquex.parse`, `publish_script` validates Lua via `BDS.Scripting.validate` | **Resolved:** validation gates added to `publish_template/1` and `publish_script/1`, invalid content returns `{:error, {:invalid_liquid|:invalid_script, reason}}`, 4 tests added |
 | A1-9 | ~~17 preset colors + custom hex in tag picker~~ | editor_tags.allium | `ColourPicker` hook + popover with 17 preset swatches grid and custom hex input, wired to both create and edit forms | **Resolved:** replaced native `<input type="color">` with `ColourPickerPopover` component (17 presets, custom hex #RRGGBB, immediate selection), JS hook for click-away dismiss, 1 test added |
-| A1-10 | Template file written on create | engine_side_effects.allium:151-153 | Draft templates have `file_path=""` | Fix code: write template file on create |
+| A1-10 | ~~Template file written on create~~ | engine_side_effects.allium:151-153 | `create_template` now computes `file_path` and writes template file with YAML frontmatter on create | **Resolved:** `create_template/1` writes `templates/{slug}.liquid` on create, `next_template_file_path` always computes path, 1 test added |
 | A1-11 | Graceful shutdown with inflight request tracking | preview.allium:47-48 | Kills acceptor process, no inflight tracking | Fix code: track inflight requests, drain before shutdown |
 | A1-12 | Real Pagefind integration for search | generation.allium:208 | Stub only: `pagefind-ui.js` is one-liner, `PagefindUI` never defined, search-runtime.js silently bails, client-side search non-functional | Fix code: bundle real Pagefind, build proper fragment index, wire PagefindUI |
 | A1-13 | Git sidebar shows only "Working tree" placeholder | sidebar_views.allium:651-770 | `sidebar.ex:782-798` returns single entity_list item; `BDS.Git` has full status/diff/commit/history/fetch/pull/push/prune_lfs but sidebar doesn't use it | Fix code: wire sidebar `git_view/0` to `BDS.Git` — render branch, ahead/behind, status file list, commit input, history entries, action buttons per spec |