Move fixed_filter_json from g3-core to g3-cli

Properly separates UI display concern from core library:
- fixed_filter_json module now lives in g3-cli (UI layer)
- UiWriter trait gains filter_json_tool_calls() and reset_json_filter() methods
- g3-core delegates filtering to UI layer via trait methods
- Different UiWriter implementations can choose their own filtering behavior
- ConsoleUiWriter filters JSON tool calls for clean terminal display
- MachineUiWriter/NullUiWriter use default pass-through

Benefits:
- Proper separation of concerns
- Core stays clean without display-specific logic
- Testability - filter can be tested independently in g3-cli

.g3/sessions/ok_awesome_can_you_commit_ca89d518008247ee/context_summary.txt

@@ -0,0 +1,16 @@
+103104-TgR, sys,   4K 🟡, You are G3, an AI programming agent of the same skill level as a seasoned engineer at a major technology company. You an
+103104-Ugn, sys,   5K 🟠, 📚 Project README (from README.md):  # G3 - AI Coding Agent  G3 is a coding AI agent designed to help you complete tasks 
+, usr,   0K 🟢, [Session Resumed]  Previous session summary: ## Move fixed_filter_json to g3-cli - Complete  ### Summary  Successfully m
+103203-esQ, usr,   0K 🟢, Task: OK awesome, can you commit the current changes and then read agents/fowler.md for prompting on refactoring hygiene
+103206-mKT, ass,   0K 🟢, I'll commit the current changes first, then read the fowler.md file and apply its guidelines.  {"tool": "shell", "args":
+103206-Ols, usr,   0K 🟢, Tool result: ❌ Command failed: bash: line 0: cd: /Users/jimbob/g3: No such file or directory
+103206-aug, ass,   0K 🟢, {"tool": "read_file", "args": {"file_path":"/Users/jimbob/g3/agents/fowler.md"}}
+103206-OLG, usr,   0K 🟢, Tool result: ❌ Failed to read file '/Users/jimbob/g3/agents/fowler.md': No such file or directory (os error 2)
+103210-eij, ass,   0K 🟢, Let me find the correct working directory first.  {"tool": "shell", "args": {"command":"pwd && ls -la"}}
+103210-Rnv, usr,   0K 🟢, Tool result: /Users/dhanji/src/g3 total 376 drwxr-xr-x@ 22 dhanji  staff     704 22 Dec 10:30 . drwxr-xr-x@  8 dhanji  s
+103212-cNH, ass,   0K 🟢, {"tool": "shell", "args": {"command":"cd /Users/dhanji/src/g3 && git status"}}
+103212-Nhy, usr,   0K 🟢, Tool result: On branch main Your branch is ahead of 'origin/main' by 3 commits.   (use "git push" to publish your local 
+103213-RBp, ass,   0K 🟢, {"tool": "read_file", "args": {"file_path":"/Users/dhanji/src/g3/agents/fowler.md"}}
+103213-Ghp, usr,   1K 🟡, Tool result: 📄 File content (151 lines): You are fowler, a specialized software refactoring agent, named after Martin Fo
+
+--- TOTAL:  12K / 200K (6.3%) ---