Editor: quick fixes, completion, navigation while typing, and split-pane drag (#109)

* feat(editor): Drag tabs and files between split panes

HTML5 drag and drop never reaches the webview while native file drop is
enabled, so tab, project-file and changelist drags did nothing. They now
run on pointer events:

- Drag an editor tab onto another pane, or onto a pane's edge to split it.
- Drag files from the Project view into an editor pane (center opens them
  there, an edge opens them in a new split).
- Drag files between changelists in the Commit view.
- "Drag-and-drop with Alt pressed only" applies to tabs and stripe buttons.

* fix(lsp): Deliver server settings and start servers on a supported JDK

- workspace/configuration answers a server's own section (basedpyright)
  from its settings block; basedpyright runs in "standard" mode and keeps
  auto search paths on, so `src/` layouts resolve from `tests/`.
- jdtls: formatting follows the editor indent, calls complete without
  guessed arguments, and JDK internals stay out of completion.
- `max-java` in a language server config picks an installed JDK no newer
  than that (kotlin-language-server fails on JDK 25).
- Server initialization may take up to 5 minutes (first Gradle import).
- `lsp_resend_diagnostics` re-emits stored diagnostics after a reload.
- Spelling only checks declared names (not called methods like
  `substring`) and accepts plurals of known software terms.

* feat(editor): Quick fixes, completion and navigation while typing

Quick fixes
- Errors get a red quick-fix bulb; Apply Quick Fix (⌥⇧↵) fixes the most
  severe problem at the caret, and the error hover offers the fix directly.
- Code generated by a code action is re-indented to the file's style.
- Python: Implement abstract methods (⌃I or the bulb) from the bases.
- Duplicate code actions are listed once.

Completion
- Overloads sharing a name, and a name importable from several modules,
  are no longer merged into one entry.
- Auto-import entries show the module they import from.
- Call snippets without a stop (`new ArrayList<>()`) leave the caret inside
  the parentheses with parameter info, or past them when nothing takes
  arguments; parameter info also opens after server call snippets.
- The selected item is resolved ahead of acceptance, so its auto-import
  is applied (rust-analyzer).

Navigation and diagnostics
- Language server requests wait for pending edits, so Go to Declaration
  right after typing answers for the current text; an empty answer right
  after an edit is retried while the server catches up.
- Diagnostics come back after a window reload; error underlines stay
  visible under typo / unused highlighting.
- Implementation gutter markers no longer refresh in a loop while the
  server reports progress.
- A missing alternative server no longer shows as a server error.

* chore(lint): Skip agent worktrees under .claude

* fix(editor): Skip cancelled LSP requests and limit generated-code reformat

- Requests cancelled while waiting for pending edits are not sent.
- Code generated by an action is reformatted per changed hunk, so an added
  import doesn't reformat the code between it and the generated lines.
- A long busy spell caused by a settle refresh re-runs it only once.
- Files dropped on a file row of another changelist move to that changelist.
- Python Implement methods: a nested class without bases ends the lookup,
  class bodies continue through unindented string lines, and
  `@abstractproperty` stubs become `@property`.
- Resend diagnostics goes through the host ops, and custom servers get
  `max_java`.

* fix(editor): Rank the exact type first in Java constructor completion

jdtls appends the call or body to filterText (`String(${0})`); matching
on the label instead lets typing `String` rank `String` above
`StringBuilder` and the other types sharing its sort text.

* fix(editor): List identical completion items once

kotlin-language-server repeats a class once per classpath entry declaring
it, so `String()` and `String` were listed three times each.

* fix(editor): Keep the internal cancellation message out of the UI text catalog

src/editor/core/controller.ts

@@ -52,6 +52,7 @@ import {
   removePane,
   reopenClosed,
   setActivePane,
+  splitAtEdge,
   sortTabs,
   splitPane,
   tabOptions,
@@ -784,7 +785,7 @@ export class EditorController implements SlotHost {
     this.navSuppress++;
     try {
       let s = useTabs.getState();
-      let paneId = s.activePane;
+      let paneId = o.pane && s.panes[o.pane] ? o.pane : s.activePane;
       if (o.side) {
         const right = neighbourPane(s, paneId);
         if (right) paneId = right;
@@ -799,7 +800,7 @@ export class EditorController implements SlotHost {
       }
       const found = findTab(s, input.key, paneId);
       let tabId: string;
-      if (found && (!o.side || found.paneId === paneId)) {
+      if (found && (!(o.side || o.pane) || found.paneId === paneId)) {
         paneId = found.paneId;
         s = activateTab(setActivePane(s, paneId), paneId, found.tab.id);
         if (!o.preview) s = promoteTab(s, paneId, found.tab.id);
@@ -935,6 +936,20 @@ export class EditorController implements SlotHost {
     if (slot?.view) slot.focus();
     else if (slot) slot.wantsFocus = true;
   }
+  /** Files dropped on an editor: opened in that pane, or in a new split at `edge`. */
+  async openFilesIn(paths: readonly string[], paneId: string, edge: SplitEdge | "center") {
+    const s = useTabs.getState();
+    if (!s.panes[paneId] || !paths.length) return;
+    let target = paneId;
+    if (edge !== "center") {
+      const r = splitAtEdge(s, paneId, edge);
+      useTabs.setState(r.state, true);
+      target = r.paneId;
+    }
+    for (const [i, path] of paths.entries()) await this.openFile(path, { pane: target, focus: i === paths.length - 1 });
+    const pane = useTabs.getState().panes[target];
+    if (pane && !pane.tabs.length) this.apply((st) => removePane(st, target));
+  }
   /** IDEA "Move to Opposite Group"; without a split, "Split and Move Right". */
   moveToOpposite(paneId: string, tabId: string) {
     const target = neighbourPane(useTabs.getState(), paneId);