fix(extended-context): suffix the Fable tier and default it on 1M launches

The previous commit assumed Claude Code's fable resolver strips [1m] and
therefore never wrote the suffix into ANTHROPIC_DEFAULT_FABLE_MODEL. That
premise only holds when ANTHROPIC_BASE_URL is unset or points at
api.anthropic.com. Behind a proxy (CLIProxy, headroom, ...) Claude Code
2.1.259 does the opposite:

- the fable alias resolver passes the env value through untouched, so a
  saved `claude-fable-5-1[1m]` reaches the model picker as-is;
- the context-window resolver grants 1M unconditionally when the model id
  carries [1m], and otherwise trusts a natively-1M model only when the base
  URL is first-party. Bare `claude-fable-5-1` via 127.0.0.1 is clamped to
  200k even though CLIProxy's /v1/models advertises max_input_tokens 1M.

So the suffix is the only thing that turns the long window on for CCS, and
stripping it from the Fable key is what kept `ccs claude --model fable` at
200k. A headroom settings profile with the suffix saved on that key showed
the 1M window in the same Claude Code build, which is how the inversion was
caught.

Changes:

- Drop the suffix-stripping key guard; ANTHROPIC_DEFAULT_FABLE_MODEL now
  receives and keeps [1m] exactly like the opus/sonnet tiers.
- On a long-context launch (explicit --1m, or a saved [1m] on any Anthropic
  tier key) fill a missing Fable tier with the catalog Fable model plus
  [1m]. The model-neutral claude profile pins no Fable model, so `--model
  fable` used to fall back to Claude Code's bare default and lose the window
  even when every other tier asked for 1M. An explicit mapping always wins,
  --no-1m never fills, and providers without a catalog Fable model are left
  alone.
- Add getDefaultFableTierModel() to the model catalog for that default.

Verified with a stub Claude binary that dumps its environment:

  ccs claude --model fable          -> ANTHROPIC_DEFAULT_FABLE_MODEL=claude-fable-5-1[1m]
  ccs claude --1m                   -> ANTHROPIC_DEFAULT_FABLE_MODEL=claude-fable-5-1[1m]
  ccs claude --no-1m --model fable  -> no Fable tier written, ANTHROPIC_MODEL stripped

tests/unit/shared/extended-context-utils.test.ts

@@ -4,7 +4,6 @@ import {
   ANTHROPIC_MODEL_ENV_KEYS,
   EXTENDED_CONTEXT_MODEL_ENV_KEYS,
   applyExtendedContextPreferenceToAnthropicModels,
-  envKeyAcceptsExtendedContextSuffix,
   hasAnthropicExtendedContextEnabled,
   isAnthropicModelEnvKey,
   isExtendedContextModelEnvKey,
@@ -37,22 +36,17 @@ describe('extended-context model env keys', () => {
     expect(isExtendedContextModelEnvKey('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(true);
     expect(isAnthropicModelEnvKey('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(false);
   });
-
-  it('marks the fable tier key as suffix-stripping', () => {
-    expect(envKeyAcceptsExtendedContextSuffix('ANTHROPIC_DEFAULT_FABLE_MODEL')).toBe(false);
-    expect(envKeyAcceptsExtendedContextSuffix('ANTHROPIC_MODEL')).toBe(true);
-    expect(envKeyAcceptsExtendedContextSuffix('ANTHROPIC_DEFAULT_OPUS_MODEL')).toBe(true);
-    expect(envKeyAcceptsExtendedContextSuffix('CLAUDE_CODE_SUBAGENT_MODEL')).toBe(true);
-  });
 });
 
 describe('applyExtendedContextPreferenceToAnthropicModels', () => {
-  it('never writes [1m] into the fable tier key and strips a saved one', () => {
+  it('writes [1m] into every managed key, the fable tier included', () => {
+    // Behind a proxy base URL Claude Code clamps a bare Fable id to 200k, so the
+    // fable tier needs the suffix exactly like the opus/sonnet tiers do.
     const env = applyExtendedContextPreferenceToAnthropicModels(
       {
         ANTHROPIC_MODEL: 'claude-fable-5-1',
         ANTHROPIC_DEFAULT_OPUS_MODEL: 'claude-opus-5',
-        ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
+        ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1',
         CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1',
       },
       true
@@ -61,7 +55,7 @@ describe('applyExtendedContextPreferenceToAnthropicModels', () => {
     expect(env).toEqual({
       ANTHROPIC_MODEL: 'claude-fable-5-1[1m]',
       ANTHROPIC_DEFAULT_OPUS_MODEL: 'claude-opus-5[1m]',
-      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1',
+      ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]',
       CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1[1m]',
     });
   });
@@ -83,7 +77,7 @@ describe('applyExtendedContextPreferenceToAnthropicModels', () => {
     });
   });
 
-  it('honors a caller compatibility predicate on top of the key guard', () => {
+  it('honors a caller compatibility predicate', () => {
     const env = applyExtendedContextPreferenceToAnthropicModels(
       {
         ANTHROPIC_MODEL: 'claude-opus-5',
@@ -99,10 +93,13 @@ describe('applyExtendedContextPreferenceToAnthropicModels', () => {
     });
   });
 
-  it('reads saved intent from the subagent key too', () => {
+  it('reads saved intent from any managed key', () => {
     expect(
       hasAnthropicExtendedContextEnabled({ CLAUDE_CODE_SUBAGENT_MODEL: 'claude-fable-5-1[1m]' })
     ).toBe(true);
+    expect(
+      hasAnthropicExtendedContextEnabled({ ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1[1m]' })
+    ).toBe(true);
     expect(
       hasAnthropicExtendedContextEnabled({ ANTHROPIC_DEFAULT_FABLE_MODEL: 'claude-fable-5-1' })
     ).toBe(false);