docs: sweep to the Anaconda 2026.06 baseline and measured container sizes

[mmcky]

The documentation is a release behind the containers, and the CHANGELOG has drifted from the merge history. Found in the 2026-07 maintenance audit.

1. Eight locations state the containers pin Anaconda 2025.12; both ship anaconda=2026.06

Ground truth is containers/quantecon/environment.yml:11, migrated in #95.

Stale locations: containers/README.md:18, containers/quantecon/README.md:15 and :107, containers/quantecon-build/README.md:26 and :82, docs/ARCHITECTURE.md:12, docs/CONTAINER-GUIDE.md:9, PLAN.md:14 and PLAN.md:74.

PLAN.md:74 is the repo's stated dependency policy, so a maintainer following it would pin the containers back to a superseded baseline — exactly the drift #28 exists to prevent.

2. The CHANGELOG asserts the old pin and is missing five entries

CHANGELOG.md:13 and :19 still assert anaconda=2025.12 as the shipped pin. Separately, five of the seven commits since v0.8.0 have no CHANGELOG entry at all — including 46f3a31, the 2026.06 migration, which is already live in :latest.

Missing entries: #95, #93, #91, #90, #94.

3. Six docs still advertise "~8GB / ~3GB" and "~60% smaller"

The measured figures — already correct in README.md:147 and docs/ARCHITECTURE.md:15 — are 8.3 GB / 7.1 GB on disk (~3.2 / ~2.9 GB compressed). That is roughly a 14% saving, not 60%. The v0.8.0 doc sweep skipped everything under containers/.

Stale locations: docs/QUICK-REFERENCE.md:22-23, setup-environment/README.md:34-35, containers/README.md:9-10 and :35, containers/VALIDATION.md:17-18, containers/quantecon-build/README.md:18, .github/copilot-instructions.md:33-34.

4. "Minimal TexLive" is false

Diffing the apt lists — containers/quantecon/Dockerfile:8-50 against containers/quantecon-build/Dockerfile:8-50 — shows the lean image drops only texlive-luatex and adds graphviz. Both texlive-latex-extra and texlive-fonts-extra are present in each.

That claim is the stated reason the lean image exists and the basis of every "use quantecon-build for CI" recommendation. Stale at containers/README.md:33, containers/VALIDATION.md:18, containers/quantecon-build/README.md:15.

5. PLAN.md lists three completed items

Item 3 (Dependabot conda grouping) is already done — dependabot.yml:44-70 ignores all ten pinned packages plus anaconda. Item 4's PRs #86/#87 are closed. Item 13's #90 is merged (0668b42). The "Open issues disposition" table also predates #96–#100 and #102.

Checklist

• 2025.12 → 2026.06 across the eight locations, including both PLAN.md references
• Rewrite the #28 [Unreleased] CHANGELOG entry in past tense
• Add [Unreleased] entries for Migrate both containers to the Anaconda 2026.06 baseline #95, Add PROJECT-OPTIMIZE-PREVIEWS.md: fast preview builds research and roadmap #93, Rewrite PLAN.md as the repo's working plan (July 2026) #91, ci: bump the github-actions-major group across 4 directories with 2 updates #90, ci: bump the github-actions group across 2 directories with 5 updates #94
• Propagate the measured size pairs to the six stragglers; delete "~60% smaller" and "faster CI pulls"
• Correct the "Minimal TexLive" wording in three files
• Strike PLAN items 3/4/13; add dispositions for New action: sync-notebooks (internal git) — standardize notebook publishing #96–testing: publish/preview/cache action logic has no automated tests #100 and hansen_singleton_1983: build-time pd.read_csv of a vendored CSV over a raw-GitHub URL flakes on HTTP 429 #102
• Add PLAN.md to the CONTRIBUTING doc-update matrix

This is a prerequisite for trusting anything else in the docs, so it is worth landing early even though nothing depends on it mechanically.