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.

README.md

@@ -0,0 +1,16 @@
+# itelescope
+
+Reference and review of the [iTelescope.net](https://www.itelescope.net/) remote
+telescope network: every telescope, its specs, what it is good at, and which one to
+book for a given target.
+
+- **[TELESCOPES.md](TELESCOPES.md)**: the full review, grouped by observatory, with a
+  "choosing a telescope" guide at the end.
+- **[data/itelescope-telescopes.csv](data/itelescope-telescopes.csv)**: snapshot of
+  the network's maintained specs sheet (source of truth for the numbers).
+- **state/**: project state under the Default Workflow.
+
+Sources: the iTelescope support article
+([telescope summary](https://support.itelescope.net/support/solutions/articles/247371))
+and the network's maintained Google Sheet. The launchpad at
+[go.itelescope.net](https://go.itelescope.net/) is login-only.