feat: add token counting, markdown format, and YAML escaping fixes

- Add token counting module with tiktoken support and fallback approximation
- Add o200k_harmony encoding for newer models
- Add warning when --token-encoding used without --tokens
- Fix YAML escaping for \n, \r, \0, \x85, \u2028, \u2029 in filenames
- Add markdown output format with language-aware code fences
- Add comprehensive tests for tokens (23), markdown (56), YAML escaping (11)

Author: nikolay-e

CLAUDE.md

@@ -69,14 +69,9 @@ treemapper . --tokens --copy          # tokens + clipboard
 
 **Encodings:**
 - `o200k_base` (default) — GPT-4o tokenizer
+- `o200k_harmony` — GPT-4.1/newer models tokenizer
 - `cl100k_base` — GPT-4/GPT-3.5 tokenizer
 
-**Installation:**
-```bash
-pip install treemapper[tokens]        # exact counts with tiktoken
-pip install treemapper                # fallback: chars/4 approximation
-```
-
 Token count is displayed on stderr only when connected to a TTY (won't break pipes).
 
 ## Clipboard Support

pyproject.toml

@@ -70,6 +70,7 @@ classifiers = [
 dependencies = [
     "pathspec>=0.11,<2.0",
     "pyyaml>=6.0.2,<8.0",
+    "tiktoken>=0.7,<1.0",
 ]
 
 [project.urls]
@@ -79,9 +80,6 @@ Homepage = "https://github.com/nikolay-e/treemapper"
 treemapper = "treemapper.treemapper:main"
 
 [project.optional-dependencies]
-tokens = [
-    "tiktoken>=0.7,<1.0",
-]
 dev = [
     # Testing
     "pytest>=7.0,<9.0",