auto-load extension i18n catalogs; add the missing tab-title ones

Five builtins (tickets, decisions, git, pql, problems) declared a
localized tab title but shipped no catalog and weren't in the hand-kept
preload list, so each logged "namespace not registered" on boot.
ExtensionManager now loads the i18n namespace of every localized
TabContribution when its extension activates — no manual list edit for a
new tab — and the five missing en_US catalogs are added.

T-155.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/kernel/src/i18n/catalog/builtin.decisions_en_us.json

@@ -0,0 +1,3 @@
+{
+  "tab.title": { "translation": "Decisions" }
+}

lib/kernel/src/i18n/catalog/builtin.git_en_us.json

@@ -0,0 +1,3 @@
+{
+  "tab.title": { "translation": "Git" }
+}

lib/kernel/src/i18n/catalog/builtin.pql_en_us.json

@@ -0,0 +1,3 @@
+{
+  "tab.title": { "translation": "pql" }
+}

lib/kernel/src/i18n/catalog/builtin.problems_en_us.json

@@ -0,0 +1,3 @@
+{
+  "tab.title": { "translation": "Problems" }
+}

lib/kernel/src/i18n/catalog/builtin.tickets_en_us.json

@@ -0,0 +1,3 @@
+{
+  "tab.title": { "translation": "Tickets" }
+}