clear dart doc validate-links warnings

Eight unresolved doc references and broken README-rewritten links
that surfaced under `dart doc --validate-links`:

- Library-scope refs `[spawn]`, `[openProject]` qualified to
  `[Backend.spawn]` / `[Backend.openProject]`; same treatment for
  `[resolvePaths]` / `[applyResolved]` on Toolchain.
- `[D-41]` was a decision ID, not a Dart symbol — drop the brackets.
- `[from]` from I18n.interpolated qualified to `[I18nReplacer.from]`.
- `[DefaultSurfaceMap]` was a stale name (private `_defaultSurfaceMap`
  in resolver.dart); switch to backticked path reference since
  dartdoc can't link private members.
- `[icons/]` was a directory, not a symbol; backticked path.
- README links to `legacy/`, `docs/initial-plan.md`, `decisions/`,
  `LICENSE` rewritten as absolute github.com/postmeridiem/clide URLs
  so dartdoc stops re-rooting them into the doc tree.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/kernel/src/backend.dart

@@ -1,8 +1,8 @@
 /// Manages the backend isolate lifecycle.
 ///
 /// Two-phase boot:
-///   1. [spawn] — starts the isolate, resolves toolchain (binary checks only).
-///   2. [openWorkspace] — initializes services for a specific project root.
+///   1. [Backend.spawn] — starts the isolate, resolves toolchain (binary checks only).
+///   2. [Backend.openProject] — initializes services for a specific project root.
 library;
 
 import 'dart:async';
@@ -34,7 +34,7 @@ class Backend {
   int _validateId = 0;
 
   /// Spawn the backend isolate. Returns when the toolchain is resolved.
-  /// No services are active yet — call [openWorkspace] to activate.
+  /// No services are active yet — call [openProject] to activate.
   static Future<Backend> spawn({
     required IsolateClient Function(SendPort backendPort) clientFactory,
     String? hintRoot,

lib/kernel/src/i18n/i18n.dart

@@ -136,7 +136,8 @@ class I18n extends ChangeNotifier {
   }
 
   /// [string] + naive `replaceAll` interpolation per replacer.
-  /// Matches fframe: replacers whose [from] isn't present are silent no-ops.
+  /// Matches fframe: replacers whose [I18nReplacer.from] isn't present
+  /// are silent no-ops.
   String interpolated(
     String key, {
     required String namespace,

lib/kernel/src/theme/tokens.dart

@@ -6,8 +6,8 @@ import 'package:flutter/foundation.dart';
 ///
 /// The token surface grows as features need more of it. Every token
 /// declared here must have a default resolution in
-/// [DefaultSurfaceMap] so legacy palette-only themes produce a complete
-/// SurfaceTokens without declaring the full surface.
+/// `_defaultSurfaceMap` (resolver.dart) so legacy palette-only themes
+/// produce a complete SurfaceTokens without declaring the full surface.
 @immutable
 class SurfaceTokens {
   const SurfaceTokens({

lib/kernel/src/toolchain.dart

@@ -1,8 +1,8 @@
 /// Centralized binary resolution for external tools.
 ///
-/// Resolution runs in a background isolate via [resolvePaths] to avoid
-/// blocking the merged UI/platform thread on macOS. The result is
-/// applied on the main thread via [applyResolved].
+/// Resolution runs in a background isolate via [Toolchain.resolvePaths]
+/// to avoid blocking the merged UI/platform thread on macOS. The result
+/// is applied on the main thread via [Toolchain.applyResolved].
 library;
 
 import 'dart:async';