refactor: deep review fixes round 3

- client.py:
  - Remove dead _extract_cursor second branch (unreachable code)
  - Cache SSL context as module-level _SSL_CTX (avoid re-reading CA certs)
  - Add 404 stale-fallback retry to _graphql_post (parity with GET)
  - Remove dead core.get('name')/core.get('screen_name') in fetch_user
  - Set Content-Type: application/json only for POST requests
  - Rename _to_int → _parse_int for clarity vs config._as_int
  - Add 'not thread-safe' note on module-level caches

- cli.py:
  - _fetch_and_display now accepts optional config param (fix double load)
  - Refactor user_posts to use _fetch_and_display
  - Pass config to all _fetch_and_display callers

- pyproject.toml:
  - Move xclienttransaction/requests to optional [transaction] deps
  - Add beautifulsoup4 to [transaction] optional deps

- README.md:
  - Add rateLimit config section with comments
  - Add constants.py to project structure tree

uv.lock

@@ -845,10 +845,7 @@ dependencies = [
     { name = "click", version = "8.1.8", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.10'" },
     { name = "click", version = "8.3.1", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.10'" },
     { name = "pyyaml" },
-    { name = "requests", version = "2.32.4", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
-    { name = "requests", version = "2.32.5", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.9'" },
     { name = "rich" },
-    { name = "xclienttransaction" },
 ]
 
 [package.optional-dependencies]
@@ -858,19 +855,26 @@ dev = [
     { name = "pytest", version = "9.0.2", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.10'" },
     { name = "ruff" },
 ]
+transaction = [
+    { name = "beautifulsoup4" },
+    { name = "requests", version = "2.32.4", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.9'" },
+    { name = "requests", version = "2.32.5", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.9'" },
+    { name = "xclienttransaction" },
+]
 
 [package.metadata]
 requires-dist = [
+    { name = "beautifulsoup4", marker = "extra == 'transaction'", specifier = ">=4.12" },
     { name = "browser-cookie3", specifier = ">=0.19" },
     { name = "click", specifier = ">=8.0" },
     { name = "pytest", marker = "extra == 'dev'", specifier = ">=8.0" },
     { name = "pyyaml", specifier = ">=6.0" },
-    { name = "requests", specifier = ">=2.32.4" },
+    { name = "requests", marker = "extra == 'transaction'", specifier = ">=2.32.4" },
     { name = "rich", specifier = ">=13.0" },
     { name = "ruff", marker = "extra == 'dev'", specifier = ">=0.8" },
-    { name = "xclienttransaction", specifier = ">=1.0.1" },
+    { name = "xclienttransaction", marker = "extra == 'transaction'", specifier = ">=1.0.1" },
 ]
-provides-extras = ["dev"]
+provides-extras = ["transaction", "dev"]
 
 [[package]]
 name = "typing-extensions"