feat(app): live session update + tool renderer + input_tokens migration

SessionDetail live update:
- Extract session-view-state.mjs: capture scroll position, disclosure
  (open/skill-md-open) state, and visible-UUID anchor before refresh;
  reconcile messages by UUID (in-place update, append tail only); restore
  scroll and disclosure state after DOM patch. findLastMessageAtOrAbove uses
  binary search (O(log n)) instead of linear scan.
- scrollRevision tracks user scrolls during refresh to avoid stale anchors
  overriding manual navigation.
- Throttle onScroll to one rAF per frame.

Tool renderer:
- Extract tool-renderer.js: standalone module for rendering tool call cards
  (Read/Write/Edit diffs, Bash terminal output, search results, JS/TS
  syntax highlighting). Replaces inline rendering in SessionDetail.
- tests/app-tool-renderer.test.mjs covers escaping, highlighting, and
  terminal formatting.

Input tokens semantics migration:
- Claude provider now sums input_tokens + cache_creation_input_tokens +
  cache_read_input_tokens into a single input_tokens value (was previously
  only the raw field, undercounting when cache tokens are present).
- One-time index-wide re-parse triggered when the marker
  __claude_input_tokens_include_cache_v1__ is absent and the DB already
  has token data (self-healing on first build after upgrade).
- App indexer.ts carries the same marker check for the app's build path.

Also:
- PRODUCT.md: product register (users, purpose, brand, design principles,
  accessibility targets).
- README.md: minor wording updates.

Co-Authored-By: Codex (GPT-5) <noreply@openai.com>

README.md

@@ -42,11 +42,11 @@ For live app refresh, Obelisk watches `~/.claude/projects` and `~/.codex/session
 You can use obelisk like:
 
 ```
-/obelisk-skill 上次 auth bug 最后到底改了哪些文件，为什么这么改
-/obelisk-skill 这个文件最近在哪些 sessions 里被反复修改
-/obelisk-skill 找出最近失败的 tool calls，它们分别发生在哪些任务里
-/obelisk-skill 那个 review workflow 的 subagents 各自结论是什么
-/obelisk-skill recap this week
+/obelisk 上次 auth bug 最后到底改了哪些文件，为什么这么改
+/obelisk 这个文件最近在哪些 sessions 里被反复修改
+/obelisk 找出最近失败的 tool calls，它们分别发生在哪些任务里
+/obelisk 那个 review workflow 的 subagents 各自结论是什么
+/obelisk recap this week
 ```
 
 ### Install
@@ -60,7 +60,7 @@ Or manually: copy `obelisk-skill/` into your project's `.claude/skills/`
 Then in any Claude Code session:
 
 ```
-/obelisk-skill <your question>
+/obelisk <your question>
 ```
 
 First run builds the index (~5 seconds for 100 sessions). After that it rebuilds incrementally.