content(newsletter): add issue 407

[axsaucedo]

Issue 407 leads with Part 2 of the Agentic Security & Identity series, then Uber on their MCP Gateway, Gemini 4 Argon, RRSI from Google Cloud AI Research on stopping self-improving harnesses from overfitting, and Sebastian Raschka's history of text classification up to Jev.

The hook links the Part 2 post, which only goes live once #171 merges, so that one needs to land first.

Two subjects repeat from recent issues on purpose: harness optimisation (405, 406) and Jev (405, 406). Both sections say so in the prose. Gemini and RRSI are also both Google, which the selection rules normally avoid; I kept both because they come from different groups and the owner picked them.

A second commit carries the events scout's ledger update for the week. No events.yaml changes; the scout's two proposals (AI Engineer Europe 2027, the KubeCon co-located CFP row) are still awaiting a yes.

Style lint passes with two warnings (fewer exclamations and semicolons than the corpus average, from the owner's edit), and check:voice and npm run check pass locally.

[github-actions]

Visual parity — light theme ☀️

1440x1000 — 6 of 40 routes moved.

Route	Differing pixels	Peak channel delta
contact.png	178	245/255
home.png	406	245/255
network.png	9,958	245/255
newsletter--archive--2025.png	916	154/255
newsletter--topic--llms.png	603,385	241/255
newsletter.png	200,138	241/255

420x900 — 6 of 40 routes moved.

Route	Differing pixels	Peak channel delta
contact.png	178	246/255
home.png	406	246/255
network.png	10,136	246/255
newsletter--archive--2025.png	1,106	154/255
newsletter--topic--llms.png	757,617	212/255
newsletter.png	242,501	204/255

Differing pixels locate a change; the peak channel delta sizes it. A large count with a
delta of 1–2/255 is a sub-perceptual shift, a small count at 200/255 is something a reader
would see.

Informational: label the PR visual-change to state that pixels are meant to move, or dependencies to require zero.

[github-actions]

Visual parity — dark theme 🌙

1440x1000 — 6 of 40 routes moved.

Route	Differing pixels	Peak channel delta
contact.png	178	208/255
home.png	406	225/255
network.png	9,942	220/255
newsletter--archive--2025.png	911	107/255
newsletter--topic--llms.png	600,325	236/255
newsletter.png	199,064	236/255

420x900 — 6 of 40 routes moved.

Route	Differing pixels	Peak channel delta
contact.png	178	206/255
home.png	406	225/255
network.png	10,126	220/255
newsletter--archive--2025.png	1,100	107/255
newsletter--topic--llms.png	755,126	236/255
newsletter.png	241,677	236/255

Differing pixels locate a change; the peak channel delta sizes it. A large count with a
delta of 1–2/255 is a sub-perceptual shift, a small count at 200/255 is something a reader
would see.

Informational: label the PR visual-change to state that pixels are meant to move, or dependencies to require zero.