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/PR_TEMPLATE.md

@@ -0,0 +1,35 @@
+# <feature title>
+
+> Fill this in when opening the PR. It is the summary a later documentation session
+> reads to write the docs, so make it complete and self contained.
+
+## Feature
+
+<What was built, in plain terms.>
+
+## What was achieved
+
+<The outcome. What now works that did not before.>
+
+## How to verify
+
+<Steps or commands to confirm it works.>
+
+## Tools used
+
+<Languages, libraries, commands, services involved.>
+
+## How it works
+
+<Enough detail for a documentation session to start from this PR alone: the approach,
+the key files, and how the pieces connect.>
+
+## State updated
+
+- [ ] `state/TODO.md`
+- [ ] `state/DECISIONS.md` (if a decision was made)
+- [ ] `state/ARCHITECTURE.md` (if the structure changed)
+
+## Follow ups
+
+<Anything deferred or worth doing next.>