feat: make tiktoken a required dependency

Author: nikolay-e

CLAUDE.md

@@ -72,12 +72,6 @@ treemapper . --tokens --copy          # tokens + clipboard
 - `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

@@ -74,6 +74,7 @@ classifiers = [
 dependencies = [
     "pathspec>=0.11,<2.0",
     "pyyaml>=6.0.2,<8.0",
+    "tiktoken>=0.7,<1.0",
 ]
 
 [project.urls]
@@ -83,9 +84,6 @@ 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",