Make the merged repository coherent: README, state, and internal links

The mechanical merge preserved both histories but left two repositories
sitting side by side rather than one repository. This is the part that
makes it whole.

A top-level README explains the three strands - the telescope network
and campaign, the processing code, and in-person observing plans - and
says plainly that image data does not live here, because that is the
first question anyone will have when they find a pipeline with no
pixels.

state/PROJECT.md was still describing a markdown-only reference project
whose scope explicitly EXCLUDED automating bookings and image
processing. Both of those are now most of what the project does, so the
objective, scope and key facts are rewritten to match reality.

state/DECISIONS.md records why the merge happened - the two repos were
split by chronology rather than design, and the seam was already
leaking, with the campaign's TODO citing results held in the other repo
and the pipeline's README explaining a campaign it did not contain. It
also records that the image data deliberately stays out of the
repository.

state/TODO.md gains the pipeline and observing work that previously had
nowhere to live, including the measurement that changes the pipeline
plan: per-frame processing is 2.9 seconds and the whole 24-frame session
is 1.1 minutes single-threaded, so a scheduler earns nothing on stacking
and should be pointed at the Monte Carlo stages instead.

Internal links fixed for the new paths: pipeline/README.md referred to
session-scripts/ throughout, and itelescope/README.md pointed at a
state/ directory that is now one level up.

The .gitignore conflict between the two repositories is resolved by
combining them, with image formats ignored globally except under docs/,
where documentation figures are committed deliberately.

README.md

@@ -0,0 +1,62 @@
+# astrophotography
+
+Everything to do with taking, processing and understanding astronomical images:
+the remote telescopes, the code that turns their frames into pictures and
+measurements, and the plans for observing in person.
+
+Formed by merging the `itelescope` and `astro-pipeline` repositories, with the
+history of both preserved.
+
+## Layout
+
+| Directory | What it is |
+|---|---|
+| **[itelescope/](itelescope/)** | The iTelescope.net remote telescope network: a review of every scope, a southern-target guide, the observing plans, and the points drain campaign |
+| **[pipeline/](pipeline/)** | The processing and analysis code. Calibration, stacking, plate solving, rendering and the science analyses |
+| **[observing/](observing/)** | Plans for observing in person. Currently the total solar eclipse of 12 August 2026 from Menorca |
+| **[state/](state/)** | Project state under the Default Workflow: objective, current work, decisions, working notes |
+| **[docs/](docs/)** | The Default Workflow itself: branching, commits, documentation policy, cost control |
+
+## Start here
+
+- Planning or reviewing a remote imaging run: **[itelescope/CAMPAIGN.md](itelescope/CAMPAIGN.md)** and **[itelescope/TELESCOPES.md](itelescope/TELESCOPES.md)**
+- Processing a session's data: **[pipeline/README.md](pipeline/README.md)**
+- What is happening right now: **[state/TODO.md](state/TODO.md)**
+- Why something was done a particular way: **[state/DECISIONS.md](state/DECISIONS.md)**
+
+## Where the image data lives
+
+**Not in this repository.** A single calibrated frame is 61 MB and a session
+runs to several gigabytes, so sessions stay on disk and the code finds them
+through the `ASTRO_SESSION` environment variable:
+
+```
+set ASTRO_SESSION=...\NGC5128\20260721
+python pipeline/stack.py
+```
+
+Each session directory carries its own `METHODS.md` describing what was done to
+that data and what was found, written for a reader who was not there. The code
+lives here; the pixels and the account of them live with the data.
+
+## Things learned the hard way
+
+Recorded because each cost real time or real money, and because each is a
+requirement for anything built next rather than a curiosity:
+
+- **Measure whether a core is saturated before buying time to fix it.** A
+  foreground star 69 arcsec from Centaurus A's nucleus was mistaken for the
+  galaxy, and a telescope booking was made to solve a problem that did not
+  exist. Filter the stars out of the measurement first.
+- **Vet moving-object candidates in detector coordinates.** Registration holds
+  the sky still, so it drags sensor defects across the frame on perfectly
+  straight, constant-rate tracks. Hot pixels are better-behaved asteroids than
+  real asteroids. One cut took 141 confident spurious detections to zero.
+- **Never compare an aperture magnitude against a point-source catalogue
+  without checking the source is a point.** A resolved object looks exactly like
+  a 2.8 magnitude outburst.
+- **Never fit a sky background to a field the target fills.** A plane fitted
+  around a large galaxy eats its halo, measured at -17.9 ADU/px. Fit the
+  background and a source model together.
+- **A photographic ND filter is not a solar filter.** It passes the infrared
+  that carries the heat.