Add on-canvas page counter with luminance-based color

[JoshCLWren]

Summary

Adds an on-canvas page counter that renders a current/total fraction in the bottom-right of the canvas. Text color auto-flips between black and white based on the mean luminance of the displayed page so it stays legible against both light and dark art.

Behavior

• Format: N/T (e.g. 1/32 on the first page, 32/32 on the last).
• Color: white text on dark pages (mean luminance < 128), black on light pages.
• Hidden on text/info-overlay pages, single-page sources, and when no source is loaded.
• Hidden on info pages rendered alongside a cover (matches the existing info-overlay hide pattern).
• Re-renders on every page turn; canvas.delete("all") paths reset the counter id.

Implementation

• self._page_counter_id state alongside the existing canvas image id.
• _page_counter_text() returns the fraction or None to hide.
• _page_counter_color() downscales the current PIL image to 32x32 grayscale and uses PIL.ImageStat.Stat for the mean luminance.
• _update_page_counter() creates/replaces a canvas.create_text item at the bottom-right anchor.
• _clear_page_counter() removes the item safely (swallows TclError).
• All four wire-up points: _display_cached_image, _display_image_fast, plus no-source/info-overlay branches in _render_current, _render_current_sync, and _render_info_with_image.

Testing

• New tests/test_page_counter.py (17 tests): counter renders, updates across next_page, hides on text/info pages, color flips correctly on dark vs light pages, defaults to white without PIL, suppresses on single-page sources, handles stale ids, and clears on no-source render paths.
• Full suite: 488 tests pass (up from 471); coverage stays at the 95.79% baseline (no regression).
• Lint (make lint): clean.
• Tested with .cbz archive (no UI smoke for .cbr needed — feature is rendering-only and uses the same code path as CBZ).

Docs

• Added to docs/PARITY.md under the "Completed Parity" → "Navigation" section, treated as CDisplay parity per design decision.

Summary by CodeRabbit

• New Features

  • Added a bottom-right page counter displaying the current page and total pages.
  • Counter automatically hides on text-only, single-page, and information-overlay views.
  • Counter color adjusts between black and white for readability against the page.

• Documentation

  • Documented the page counter in the feature parity guide.

• Tests

  • Added coverage for counter visibility, updates, readability, and rendering edge cases.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 523bedc8-b7d5-4e79-b0f2-8f45508614b3

📥 Commits

Reviewing files that changed from the base of the PR and between b1f5b87 and 64ae07f.

📒 Files selected for processing (1)

• cdisplayagain.py

📝 Walkthrough

Walkthrough

Changes

The viewer adds a bottom-right current/total page counter for multi-page image content. It selects black or white text from page luminance, updates the counter across image rendering paths, clears it for text and info pages, documents the feature, and adds comprehensive tests.

Page counter overlay

Layer / File(s)	Summary
Counter state and appearance cdisplayagain.py, docs/PARITY.md	ComicViewer tracks the counter canvas item, computes visibility and "{current}/{total}" text, selects luminance-based colors, and documents the overlay.
Rendering path integration cdisplayagain.py	Cached and fast-preview image rendering updates the counter; text pages, missing sources, and information overlays clear it.
Counter behavior validation tests/test_page_counter.py	Tests cover visibility, text updates, color fallback, stale canvas items, TclError handling, and rendering cleanup.Estimated code review effort: 3 (Moderate)

Sequence Diagram(s)

sequenceDiagram
  participant ComicViewer
  participant PageSource
  participant Canvas
  ComicViewer->>PageSource: read current page and total page count
  ComicViewer->>Canvas: render current image
  ComicViewer->>Canvas: create or replace page counter
  ComicViewer->>Canvas: clear counter for text or info-overlay pages

Loading

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 70.59% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: adding an on-canvas page counter with luminance-based color selection.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/page-counter

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@cdisplayagain.py`:
- Around line 1272-1305: Update _update_page_counter to call _clear_page_counter
at the start instead of duplicating the page-counter deletion and
exception-handling logic. Preserve the existing behavior of resetting
_page_counter_id before rendering or returning when no text is available.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5fbb6e37-a216-4662-98e5-3b51fe162bf8

📥 Commits

Reviewing files that changed from the base of the PR and between 9319449 and b1f5b87.

📒 Files selected for processing (3)

• cdisplayagain.py
• docs/PARITY.md
• tests/test_page_counter.py