Promote CIRCUS from _wip to top-level project

Moves CIRCUS from _wip/CIRCUS to CIRCUS/ with full ROM build:
- Adds header.s, chr.s, linker.cfg (HEADER+PRG+CHR segments)
- Updates Makefile to build and verify reconstructed.nes vs rom.nes
- Adds rom.nes copy + copilot/rom.nes symlink per repo convention
- Verified byte-identical build

Updates root OVERVIEW.md:
- Removes CIRCUS from _wip skeleton table (25 -> 23 skeletons)
- Adds CIRCUS as #12 in numbered inventory (BYTE-IDENTICAL, Pass 2/3)
- Updates summary count from 11 to 12 projects

CIRCUS/copilot/symbols.inc

@@ -0,0 +1,108 @@
+; =============================================================================
+; Nintendo Entertainment System hardware symbols
+; =============================================================================
+
+; -----------------------------------------------------------------------------
+; PPU registers
+; -----------------------------------------------------------------------------
+
+PPUCTRL             = $2000
+PPUMASK             = $2001
+PPUSTATUS           = $2002
+OAMADDR             = $2003
+OAMDATA             = $2004
+PPUSCROLL           = $2005
+PPUADDR             = $2006
+PPUDATA             = $2007
+
+OAMDMA              = $4014
+
+; -----------------------------------------------------------------------------
+; Controller ports
+;
+; $4016:
+;   Write: controller strobe
+;   Read:  controller port 1
+;
+; $4017:
+;   Read:  controller port 2
+;   Write: APU frame counter
+; -----------------------------------------------------------------------------
+
+JOY1                = $4016
+JOY2                = $4017
+
+; -----------------------------------------------------------------------------
+; APU pulse channel 1
+; -----------------------------------------------------------------------------
+
+APUPULSE1CTRL       = $4000
+APUPULSE1SWEEP      = $4001
+APUPULSE1TIMERLO    = $4002
+APUPULSE1TIMERHI    = $4003
+
+; -----------------------------------------------------------------------------
+; APU pulse channel 2
+; -----------------------------------------------------------------------------
+
+APUPULSE2CTRL       = $4004
+APUPULSE2SWEEP      = $4005
+APUPULSE2TIMERLO    = $4006
+APUPULSE2TIMERHI    = $4007
+
+; -----------------------------------------------------------------------------
+; APU triangle channel
+; -----------------------------------------------------------------------------
+
+APUTRIANGLECTRL     = $4008
+APUTRIANGLETIMERLO  = $400A
+APUTRIANGLETIMERHI  = $400B
+
+; -----------------------------------------------------------------------------
+; APU noise channel
+; -----------------------------------------------------------------------------
+
+APUNOISECTRL        = $400C
+APUNOISEPERIOD      = $400E
+APUNOISELENGTH      = $400F
+
+; -----------------------------------------------------------------------------
+; APU DMC channel
+; -----------------------------------------------------------------------------
+
+APUDMCCTRL          = $4010
+APUDMCDIRECT        = $4011
+APUDMCADDR          = $4012
+APUDMCLENGTH        = $4013
+
+; -----------------------------------------------------------------------------
+; APU status and frame counter
+;
+; $4015:
+;   Write: enable or disable the five APU channels
+;   Read:  channel and interrupt status
+;
+; $4017:
+;   Write: APU frame-counter mode and IRQ inhibit
+;   Read:  controller port 2
+; -----------------------------------------------------------------------------
+
+APUSTATUS           = $4015
+APUFRAMECOUNTER     = $4017
+
+; -----------------------------------------------------------------------------
+; Controller masks
+; -----------------------------------------------------------------------------
+
+PAD_RIGHT           = $01
+PAD_LEFT            = $02
+PAD_DOWN            = $04
+PAD_UP              = $08
+PAD_START           = $10
+PAD_SELECT          = $20
+PAD_B               = $40
+PAD_A               = $80
+
+PAD_HORIZONTAL      = PAD_LEFT | PAD_RIGHT
+PAD_VERTICAL        = PAD_UP | PAD_DOWN
+PAD_DPAD            = PAD_HORIZONTAL | PAD_VERTICAL