script: shorten jtag_* command names

Drop the get_/set_/_pin/_list noise from the JTAG commands (e.g.
jtag_get_probes_list -> jtag_probes, jtag_set_spi_cs_pin -> jtag_spi_cs,
jtag_spi_rd_wr -> jtag_spi_xfer). jtag_open_probe -> jtag_open (not
jtag_probe, which would clash with jtag_probes under tab-completion).

Hard rename, no aliases. Updates the state-dump emitter, help text,
example script and docs accordingly.

CLAUDE.md

@@ -56,7 +56,7 @@ Adding a feature usually means adding a new script command in
 
 Move forward phase by phase: validate one with the user before starting
 the next. Don't break the validated path
-`jtag_open_probe → jtag_autoinit → jtag_set_mode 0 EXTEST` while
+`jtag_open → jtag_autoinit → jtag_mode 0 EXTEST` while
 refactoring.
 
 ## Key technical decisions