frontend: move shared/terminal.js+css into one-dir terminal/

Same pure structural move as the previous commit, applied to the one
other remaining genuine component in shared/src (a self-contained
widget with its own behaviour + CSS, same class as hive-btn/hive-
dialog/hive-toast/hive-menu/side-panel/tabs) -- not the CSS-foundation
files (colors/theme/base/chrome.css) or the utility modules (forms.js,
dom.js, modal.js, shadow-css.js), which aren't components and don't
fit the one-dir-per-component convention.

External callers resolve terminal.js/terminal.css only through
@hive/shared's exports map, so again the two exports targets are the
only external-facing change. index.js's own internal re-export uses a
relative path within the package, so that needed updating too. Zero
call-site changes outside @hive/shared. Verified the built dashboard
(flow.js/common.css) and agent (app.js/agent.css) bundles still
resolve both files.

frontend/packages/shared/package.json

@@ -7,13 +7,13 @@
   "main": "./src/index.js",
   "exports": {
     ".": "./src/index.js",
-    "./terminal.js": "./src/terminal.js",
-    "./tabs.js": "./src/tabs.js",
-    "./tabs.css": "./src/tabs.css",
+    "./terminal.js": "./src/terminal/terminal.js",
+    "./tabs.js": "./src/tabs/tabs.js",
+    "./tabs.css": "./src/tabs/tabs.css",
     "./colors.css": "./src/colors.css",
     "./theme.css": "./src/theme.css",
     "./base.css": "./src/base.css",
-    "./terminal.css": "./src/terminal.css",
+    "./terminal.css": "./src/terminal/terminal.css",
     "./chrome.css": "./src/chrome.css",
     "./forms.js": "./src/forms.js",
     "./dom.js": "./src/dom.js",

frontend/packages/shared/src/index.js

@@ -1,3 +1,3 @@
 // Convenience re-export so consumers can `import { create, linkify }
 // from '@hive/shared'` without naming the sub-module path.
-export { create, linkify } from './terminal.js';
+export { create, linkify } from './terminal/terminal.js';