Point chapter 3 to the 2026-27 lecture 3 slides

[ethan42]

Same as #3 for lecture 2: chapter 3, its slide questions, sources/extract/lec03.yaml, the manifest, the README and make fetch now point to the 2026-27 deck (https://progintro.github.io/assets/pdf/lec03.pdf). The 2025 deck stays linked as an alternative.

What changed in the deck (page-by-page comparison with 2025-26):

• 48 pages instead of 47. New p. 40 is a live demo («Χρειάζομαι 2-3 εθελοντές/ντριες» + ssh), so 2025 pp. 40–47 are now pp. 41–48. Page references are shifted: pyth.c 40 → 41, Leibniz π 43 → 44, the reading list 46 → 47, and the chapter's page ranges.
• p. 2: new announcements. Εργασία 0 is released after the lecture, submitted through hw.uoa.gr, deadline Wednesday 2026/11/04 23:59.
• p. 3: the Kahoot screenshot (power outage / secondary memory) is replaced by a painting. slides-lec03-power-outage comes from that screenshot, so it still cites the 2025-26 deck.
• pp. 6–7: the Byte N-1 fix, as in lecture 2.
• p. 37: «περνάμε τα ορίσματά της» became «περνάμε τις παραμέτρους (ορίσματα) της». The chapter keeps its parameter (in the definition) vs argument (in the call) distinction, so I left the text alone and noted the change in the extract notes.
• p. 45: the pi example's main is now int main(int argc, char ** argv).

make check passes and the generated lists are up to date.

Opened from socrates.