Add concrete IPO stage dates to reports

Request:
- Include the concrete T0, T1, T2, and D1 dates in every analyst report.

Changes:
- Add a Stage Calendar section to the single-IPO report generator.
- Require analyst reports to include ticker-specific T0 subscription window, T1 allotment-result date, T2 grey-market date/window, and D1 listing date.
- Update the 06106 T0 report with its concrete stage dates.
- Document the requirement in the analyst skill, README, and rule change log.

Verification:
- Ran py_compile for scripts/generate_ipo_report.py.
- Generated a 06106 dry-run report and checked the stage calendar.
- Ran git diff --check.

Next useful context:
- For 06106, T0 is 2026-06-15 to 2026-06-18, T1/T2 is 2026-06-23, and D1 is 2026-06-24.

scripts/generate_ipo_report.py

@@ -287,6 +287,46 @@ def facts_table(record: dict[str, str], stage: str) -> str:
     return "\n".join(lines)
 
 
+def stage_calendar_table(record: dict[str, str]) -> str:
+    application_start = fmt_value(record["application_start_date"])
+    application_end = fmt_value(record["application_end_date"])
+    allotment_date = fmt_value(record["allotment_results_expected_date"])
+    listing_date = fmt_value(record["listing_date"])
+    if allotment_date != "n/a":
+        t2_date = f"{allotment_date} after allotment results"
+    elif listing_date != "n/a":
+        t2_date = "trading day before D1; exact date not archived"
+    else:
+        t2_date = "n/a"
+
+    rows = [
+        (
+            "T0_prospectus",
+            f"{application_start} to {application_end}",
+            "Subscription window; use prospectus and offer terms only.",
+        ),
+        (
+            "T1_allotment",
+            allotment_date,
+            "Allotment results day; use public demand, placing demand, and allocation facts.",
+        ),
+        (
+            "T2_grey_market",
+            t2_date,
+            "Pre-listing grey-market sell window if a reliable executable source exists.",
+        ),
+        (
+            "D1",
+            listing_date,
+            "First official trading day; default sell window when T2 data is unavailable or unreliable.",
+        ),
+    ]
+    lines = ["| Stage | Concrete Date For This IPO | Meaning |", "| --- | --- | --- |"]
+    for stage, date_text, meaning in rows:
+        lines.append(f"| `{stage}` | {date_text} | {meaning} |")
+    return "\n".join(lines)
+
+
 def source_paths(record: dict[str, str], stage: str) -> list[str]:
     paths = []
     if record["prospectus_source_path"]:
@@ -367,6 +407,10 @@ def build_report(record: dict[str, str], rows: list[dict[str, str]], stage: str,
         f"- Score bucket: `{bucket}`",
         f"- Calibrated D1 positive probability: {fmt_pct_rate(metric.d1_positive_rate)} from {metric.sample_size} historical D1 labels",
         "",
+        "## Stage Calendar",
+        "",
+        stage_calendar_table(record),
+        "",
         "## Facts",
         "",
         facts_table(record, stage),