Telescope review: all 23 active iTelescope systems

Adds TELESCOPES.md, a per-observatory review of every telescope on the
iTelescope.net network with a spec block and an assessment for each, a
'choosing a telescope' use-case table, and general observations (CCD to CMOS
migration, Bin2 software limits, elevation limits, network-side calibration).

Data sourcing:
- data/itelescope-telescopes.csv is a verbatim CSV export of iTelescope's
  maintained specs Google Sheet (24 rows: 23 active scopes + T74 placeholder).
- The support article (Freshdesk 247371) supplied observatory groupings and
  minimum elevation limits; it still lists T9/T19/T31/T69 which the sheet has
  dropped - the review follows the sheet and records the discrepancy.
- go.itelescope.net is an authenticated app shell; nothing was scraped from it.

Also fills in the remaining state/ files: TODO (pending: T74 specs, retired
scope reconciliation, periodic sheet refresh), DECISIONS (source-of-truth
choice, single-document structure, no launchpad scraping), NOTES (refresh
command, CSV quirks), ARCHITECTURE (repo layout), and README.

state/NOTES.md

@@ -0,0 +1,12 @@
+# Notes
+
+> Working notes, gotchas, environment quirks, and dead ends to avoid. Free form. The
+> point is to save a future session from rediscovering something the hard way.
+
+- Refresh the specs snapshot with:
+  `curl -sL "https://docs.google.com/spreadsheets/d/1jZWkkjewOuyNC9YzQ8y2d0pO1e4T7EBeysmQMPBVSOk/export?format=csv" -o data/itelescope-telescopes.csv`
+- The CSV has multi-line cells (quoted); line count is not row count. Telescope rows
+  start `T<number>,`; observatory header rows have an empty first column.
+- Sensors are 16-bit ADC unless noted (T20's ASI2400C is 14-bit).
+- Free scopes (30 min/day): T68 (Utah), T33 (Siding Spring).
+- Minimum elevation limits come from the support article, not the sheet.