feat: add AI Signals Radar — wide-view consolidated signal matrix report

[Copilot]

Users wanted a single "wide view" showing all trending AI signals together, rather than navigating narrative sections of the existing trending report.

New report type: ai-signals / ai-signals-en

Runs in parallel with the existing trending report, consuming the same TrendingData but producing a dense, tabular snapshot designed for scanning the full signal set at a glance.

Report structure:

• Signal Matrix — full Markdown table of every identified AI project: linked name, category (🔧/🤖/📦/🧠/🔍), total stars, today's delta, signal strength (🔥🔥🔥 >1k today → ⭐ established), ≤12-word "Why It Matters"
• Top 5 Signals — strongest movers with 2-sentence breakdown
• Category Breakdown — per-category count + one-line dominant theme
• Meta Signal — cross-signal structural analysis of ecosystem direction

Wiring

File	Change
src/prompts-data.ts	buildSignalsPrompt() — zh + en prompt builders
src/i18n.ts	SIGNALS_REPORT, ISSUE_LABELS.signals, REPORT_LABELS, NOTIFY_LABELS
src/report-savers.ts	saveSignalsReport() — LLM call + file save + issue creation
src/index.ts	Wired into parallel save phase and highlights pipeline
src/generate-manifest.ts	ai-signals / ai-signals-en added to REPORT_FILES
src/github.ts	Cyan label colors for signals / signals-en
index.html	ai-signals / ai-signals-en added to sidebar LABELS

The signals report is intentionally completeness-first (all AI signals) vs. the trending report which is curation-first (narrative analysis of selected projects).