fix: resolve mypy type errors and exclude test cassettes from yamllint (#9)

* fix: resolve mypy type errors and exclude test cassettes from yamllint

- Add explicit type annotations for after_date variables in cli.py to fix
  mypy type inference errors when using datetime | None across if/elif branches
- Exclude tests/cassettes/ directory from yamllint checks since these are
  auto-generated VCR.py test fixtures with formatting that violates yamllint
  rules (long lines, indentation)

Fixes mypy errors:
  - cli.py:374 - Incompatible types in assignment (datetime | None vs datetime)
  - cli.py:529 - Incompatible types in assignment (datetime | None vs datetime)

All pre-commit hooks now pass except no-commit-to-branch (expected on master).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* refactor: address CodeRabbit review feedback

- Use explicit glob pattern `tests/cassettes/**` in yamllint config for
  clarity (instead of `tests/cassettes/`)
- Hoist datetime variable declarations in ascents and stats commands to
  improve type checker flow analysis and avoid redefinition warnings
- Declare `after_date` and `before_date` as `datetime | None` upfront
  before if/elif blocks for cleaner scoping

Addresses CodeRabbit nitpick comments on PR #9.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: dreamiurg

.yamllint.yaml

@@ -1,6 +1,9 @@
 ---
 extends: default
 
+ignore: |
+  tests/cassettes/**
+
 rules:
   line-length:
     max: 120

peakbagger/cli.py

@@ -361,6 +361,9 @@ def ascents(
 
         # Apply date filters
         filtered_ascents = ascent_list
+        # Declare date filter variables upfront for mypy type flow
+        after_date: datetime | None = None
+        before_date: datetime | None = None
         if within:
             try:
                 period = analyzer.parse_within_period(within)
@@ -516,6 +519,9 @@ def stats(
 
         # Apply date filters
         filtered_ascents = ascent_list
+        # Declare date filter variables upfront for mypy type flow
+        after_date: datetime | None = None
+        before_date: datetime | None = None
         if within:
             try:
                 period = analyzer.parse_within_period(within)